Power Supply Form Factors
Power Supply Form Factors

When building or upgrading a computer, choosing the right power supply is crucial. Power supplies come in different sizes and shapes, and they need to match the case and motherboard. It’s important for a power supply to fit properly and provide the necessary connections and stable power for all components. Power supply standards like ATX and SFX define the dimensions, power output, and connectors, making it easier to find compatible power supplies for cases and motherboards.

Additionally, power supply efficiency is important, with certifications like 80 Plus indicating a unit’s ability to reduce electricity waste and heat generation. When picking a power supply, make sure it matches the form factor of your case, provides enough power for your components, has the right connectors, and consider its efficiency rating for long-term energy savings.

A Comprehensive Guide to PSU Form Factors

The power supply unit (PSU) is the heart of a computer, pumping electrical energy to all components. However, not all PSUs fit in all systems. They come in various form factors, each with specific dimensions and specifications. Understanding these form factors is crucial when building or upgrading your PC.

ATX: The Mainstream Choice

ATX 3.0 Power Supply
ATX 3.0 Power Supply

The ATX form factor is the most common type of PSU, known for its standard dimensions and wide compatibility with most PC cases. It offers ample space for connectors and often comes with various features like modular cabling for better cable management.


The ATX PS/2 (ATX12V) is the standard ATX PSU, widely used in most desktop computers. It has a rectangular shape with specific dimensions and offers a 12V rail for powering the CPU and other components.

ATX PS/3 (ATX12V 2.x)

The ATX PS/3 is a newer version of the ATX PSU, designed to meet the increasing power demands of modern components. It features a slightly shorter depth than the ATX PS/2 and often offers higher wattage options.

SFX: Compact Power for Small Form Factor Builds

The SFX form factor is ideal for small form factor (SFF) builds, such as mini-ITX systems. It features a smaller footprint than ATX PSUs but still delivers sufficient power for most components.


The standard SFX PSU is compact and powerful, making it a popular choice for SFF enthusiasts. It often comes with a high power density, allowing for more wattage in a smaller package.


The SFX-L PSU is a slightly larger version of the SFX form factor, offering more space for additional connectors and potentially higher wattage options. It retains the compact nature of the SFX while providing increased flexibility.

Other Form Factors: Specialized Solutions

While ATX and SFX are the most common form factors, other options cater to specific needs. These include:

  • TFX (Thin Form Factor): Designed for slim cases, TFX PSUs offer a reduced height while maintaining decent power output.
  • Flex ATX: Similar to TFX, Flex ATX PSUs are designed for slim cases but with a focus on flexibility in terms of dimensions.
  • CFX (Compact Form Factor): These PSUs are typically found in pre-built systems and offer a compact design for specific case configurations.

Form Factor Comparison Table

Form FactorDimensions (W x H x D)Typical Wattage RangeCommon Use Cases
ATX PS/2 (ATX12V)150mm x 86mm x 140mm300W – 1200WStandard desktop PCs, gaming PCs, workstations
ATX PS/3 (ATX12V 2.x)150mm x 86mm x 100mm450W – 1600WHigh-performance PCs, overclocked systems
SFX125mm x 63.5mm x 100mm300W – 850WMini-ITX builds, SFF PCs
SFX-L125mm x 125mm x 63.5mm500W – 1000WSFF PCs with high power demands, compact workstations
TFX85mm x 65mm x 175mm200W – 400WSlim PCs, all-in-one systems
Flex ATX81.5mm x 40.5mm x 150mm125W – 300WUltra-slim PCs, custom builds
CFXVaries180W – 300WPre-built systems, OEM solutions

When choosing a PSU, consider your case’s compatibility, power requirements, and desired features. A well-chosen PSU will ensure stable and efficient power delivery to your system, contributing to its overall performance and longevity.

Power Supply Form Factor Descriptions

Form FactorDescriptionTypical Use Case
ATX– Most common size – Provides ample space for cooling and modularity– Full-size towers – High-performance PCs
SFX– Compact size – Ideal for small form factor cases– Mini-ITX builds – Home theater PCs
SFX-L– Slightly larger than SFX but offers more power delivery– Small form factor cases requiring more wattage
TFX– Even smaller than SFX – Limited power delivery– Very compact cases
EPS (Enterprise Power Supply)– Similar size to ATX – Focuses on high wattage delivery for multiple CPUs– High-end workstations – Servers
FlexATX– Smaller than ATX – Limited to a few expansion slots– Small form factor business desktops

Key Takeaways

  • Power supply units (PSUs) must match the case and motherboard in size, shape, and electrical specifications.
  • Industry standards such as ATX and SFX inform the compatibility of PSUs with different PC components.
  • Efficiency ratings like 80 Plus are important for energy savings and heat reduction in PCs.

Understanding Power Supply Form Factors

Selecting the right power supply unit (PSU) requires understanding form factors. These are specifications that ensure the PSU fits properly with the computer’s case and motherboard.

Defining Form Factor

Form factors refer to the physical dimensions and standards, which dictate where and how a power supply can be mounted in a computer case. These standards ensure compatibility with different motherboard form factors. Common PSU form factors include ATX, SFX, TFX, and ITX, where each serves distinct case and board sizes.

Historical Evolution

The AT form factor was the original design for computer power supplies and motherboards. Over time, ATX (Advanced Technology eXtended) became the norm, bringing standard sizes and connector types. This evolution has given rise to variations like Micro-ATX, Mini-ITX, and others, offering different sizes suitable for various needs and space constraints.

Relevance to Motherboard Design

PSU form factors are crucial for motherboard designs. The ATX12V version, for example, features a 24-pin main connector that matches ATX motherboards. SFX power supplies, though smaller, still fit into Micro-ATX and Mini-ITX cases. The compatibility between motherboard and PSU form factors determines the proper function and potential for future upgrades.

Different Types of Power Supply Units

Power supplies come in various shapes and sizes to accommodate different computer cases and system requirements. Knowing the distinctions between power supply form factors helps in selecting the right one for your build. https://www.youtube.com/embed/bUh2EZzJZRU

ATX Power Supplies

The ATX form factor is the most common design used in desktop computers. Standard ATX power supplies typically have dimensions of 150mm x 86mm x 140mm, but can vary in length. They include a 24-pin main connector and an 8-pin (or 4-pin) CPU power connector with an additional 8-pin (or 6-pin) for PCIe graphics. The ATX12V v1.x and v2.x reference different specifications for the 12-volt power distribution.

SFX and SFX-L Variants

SFX stands for Small Form Factor and is smaller than ATX power supplies, making it suitable for compact systems like mini-ITX builds. While standard SFX dimensions are approximately 100mm x 125mm x 63.5mm, the SFX-L is a larger variant at around 125mm x 125mm x 63.5mm. Despite the reduced size, these power supplies may still offer modular cables, allowing for a tidy build with only necessary cables being used.

TFX for Slim Profiles

TFX or Thin Form Factor is designed for slim or low-profile cases. These power supplies have a long, slim shape that conserves space but still provides adequate power for the system’s components. Like other power supplies, TFX units present with the essential connectors required for a basic computer build.

FlexATX and Other Small Form Factors

FlexATX is another small form factor power supply, even more compact than the SFX version. This type is often used for micro-ATX or mini-ITX systems, where space is at a premium, and the power requirements are modest. Other small form factors also include various ITX-sized power supplies tailored for specific case designs and layouts. These typically offer a solution for small-scale builds and specialized computer designs.

Power Supply Specifications and Connectors

In choosing a power supply for a computer, it’s crucial to recognize the importance of compatible cables and the right power output. This ensures that all components receive the necessary power and can operate smoothly.

Voltage and Wattage Considerations

The voltage of a power supply must match the requirements of the computer’s components. Commonly, systems will use a 12V rail for major components, but other voltages like 3.3V and 5V are also crucial for different parts of the system. The total wattage, the power a supply can deliver, should exceed the sum of all component requirements to maintain a reliable and stable system.

Connector Types

Power supply units come equipped with various connectors, each serving a specific purpose:

  • 24-pin ATX power connector: This is the main motherboard power connector.
  • 8-pin or 4-pin CPU power connector: Supplies power to the CPU.
  • PCIe power connectors (8-pin or 6-pin): Provide power to PCIe devices like graphics cards.
  • SATA power cables: Used for storage devices and some peripherals.
  • Molex connector: An older connector type used for some storage devices, fans, and other peripherals.

To function properly, components should be connected with the correct power connectors.

Modular vs. Non-Modular Designs

Power supplies can be:

  • Non-modular: All cables are permanently attached to the PSU and cannot be removed.
  • Semi-modular: Some cables, often the 24-pin ATX and CPU power, are fixed, while others can be added as needed.
  • Fully modular: All cables are detachable, allowing users to connect only the ones necessary for their build, aiding in clean cable management.

The choice depends on case space, budget, and personal preference for cable management.

Enclosures and Power Supply Compatibility

Choosing the right power supply unit (PSU) for your computer case is crucial for ensuring efficient power delivery and reliability. This section addresses how to match PSUs to different case sizes, with a focus on full-tower and mid-tower cases, and the importance of airflow and heat management.

Matching PSUs to Cases

Matching a power supply unit (PSU) to a computer case starts with identifying the form factor. Desktop power supplies typically adhere to the ATX standard, which should fit most mid-towers and full tower cases. It is important to check the case specifications to ensure compatibility. Most cases will support standard ATX PSUs, but smaller cases may require a different form factor like SFX or TFX.

Full-Tower and Mid-Tower Considerations

Full-Tower Cases: These are large and typically offer more space for components which can include bigger or multiple PSUs. A full tower is suitable for high-end gaming PCs, servers, or workstations where multiple graphics cards or drives are used.

Mid-Tower Cases: Mid-towers are the most common case type for home and office desktops. They accommodate standard ATX PSUs but have less space compared to full towers. It’s important to consider the dimensions of both the PSU and the mid-tower to avoid space-related issues.

Airflow and Heat Dissipation

Airflow is critical in keeping components cool and operating efficiently. When installing a PSU in any case, ensure it does not obstruct air circulation. Full-tower cases generally have better airflow due to their size, which allows for large or multiple fans. Mid-tower cases may have more restricted airflow, necessitating careful management of cables and components to maintain proper air movement. Heat can be particularly challenging in smaller enclosures, so selecting a PSU with high efficiency can help reduce excess heat generation.

Efficiency Ratings and Certifications

When picking a power supply for your computer, the efficiency rating is a key factor. It shows how well the unit converts AC power from the wall to DC power for the computer. Certifications like 80 Plus let you know the unit’s efficiency.

Understanding 80 Plus Standards

80 Plus is a system that tests power supply units (PSUs) to check for their efficiency. To get certified, a PSU must hit at least 80% energy efficiency at 20%, 50%, and 100% of its stated load. The standard means less energy waste and more savings on electricity bills.

Bronze to Titanium: What It Means for You

  • Bronze: At least 82% efficiency at full load.
  • Silver: At least 85% efficiency at full load.
  • Gold: At least 87% efficiency at full load.
  • Platinum: At least 89% efficiency at full load.
  • Titanium: Highest standard, over 90% efficiency.

A PSU with a higher rating like Gold, Platinum, or Titanium is more efficient. This means it wastes less electricity and operates cooler. While the initial cost might be higher, it can save money on bills over time. Choosing the right efficiency rating helps the environment and your wallet.

Choosing the Right Power Supply

Selecting the correct power supply unit (PSU) is vital for ensuring the stable operation of your computer system. Factors such as power needs, compatibility, and budget are key considerations in making an informed decision.

Power Needs and PSU Calculator

To determine the exact power your system requires, begin by using a power supply calculator. This tool considers the various components in your system and their power consumption. Brands like SilverStone offer online calculators that provide a wattage estimate necessary for your build. You simply input your hardware details, and the calculator handles the rest.

Compatibility with Hardware

PSUs come in different sizes known as form factors, with the most common being ATX and SFX. Compatibility with your computer’s hardware is a must. The form factor dictates whether the power supply will fit in your case and if it provides the right connectors for your components. Other considerations include:

  • Cable type: Modular, semi-modular, or non-modular.
  • Amperage: Sufficient amperage on the right rails (especially for the graphics card).
  • Efficiency rating: Look for 80 PLUS certification, ranging from white to titanium.

Budget and Brand Recommendations

Your budget influences your choice of power supply. There are PSU options available at various price points, but investing in a reliable power supply can save on future costs by preventing damage to other components. Renowned brands such as be quiet! and SilverStone typically offer products that strike a balance between cost and quality. Here is a simple price categorization:

  • Entry-level: Basic functions, appropriate for non-intensive use.
  • Mid-range: Improved efficiency and features for mainstream users.
  • High-end: Advanced features for enthusiasts or professional use.

When investing in a power supply, it’s not just about wattage. It’s about choosing a product that matches your system’s needs and provides the stability for all hardware components to run efficiently. With careful consideration of the power requirements, compatibility, and budget, users can select the ideal PSU for their specific setup.

Installation and Troubleshooting

Choosing the right power supply for your computer is crucial, not only for powering your PC but also for system stability. Proper installation and troubleshooting practices ensure longevity and reliability.

Installing a PSU in Your PC Build

Install your power supply unit (PSU) by aligning it with the case’s mounting area. Secure the unit with screws. Connect the 24-pin ATX motherboard connector, ensuring a firm fit. If your motherboard supports it, attach the 8-pin or 4-pin EPS12V connector for CPU power. For desktops with powerful graphics cards, don’t forget the PCIe power connectors, which could be 6-pin or 8-pin.

Common Power Supply Problems

PC builders may encounter issues such as unexpected system shutdowns or failure to start (POST). Problems can stem from inadequate power supply, cable clutter, or worn components. Signs that your power supply may be failing include noise from the PSU fan, frequent computer crashes, or electronic burning smells.

When to Upgrade Your PSU

Consider upgrading your PSU if it’s several years old or if you’re adding new hardware that demands more power. If you recently upgraded to an ATX motherboard or added high-end video cards supported by Intel or other brands, a PSU with a larger footprint and higher wattage might be necessary. Upgraders should also look for a PSU with modular cables to reduce cable clutter and improve airflow.

By adhering to these instructions, users can maintain a functional and reliable PC, addressing issues related to power supplies with confidence and accuracy.

Frequently Asked Questions

In this section, we address some of the most common queries related to power supply form factors, focusing on their different types, dimensions, and compatibility with various computer systems.

What are the different form factors available for computer power supplies?

Computer power supplies come in various shapes and sizes, tailored to fit different kinds of cases and motherboards. The most prevalent types are ATX and SFX for standard desktop PCs, TFX for slimline desktops, and EPS for servers. There are also SFX-L and micro-ATX for compact builds.

How do the dimensions of TFX power supplies compare to other form factors?

TFX power supplies are designed for slim profile desktops. They are smaller than standard ATX power supplies, which makes them well-suited for mini-towers and other space-constrained cases. The exact size might vary, but a typical TFX power supply is approximately 85mm wide, 65mm tall, and 175mm deep.

Can you explain the difference between ATX and SFX power supplies?

ATX power supplies are the standard size for most desktop computers. They are generally larger, providing more space for air circulation and larger fans, which can result in better cooling. SFX power supplies are more compact, designed for small form factor (SFF) cases. They often come with modular cables to help manage space effectively in tight builds.

Do power supply form factors impact compatibility with different types of PCs?

Yes, power supply form factors are crucial for compatibility. PCs have cases designed for specific form factors, ensuring all components fit together. For instance, a standard ATX power supply might not fit in a small form factor case that requires an SFX unit. Always check the case and motherboard specifications to ensure the correct PSU form factor.

What types of power supply form factors are commonly used in servers?

Servers typically use the EPS form factor, also known as the Extended Power Supply. This form factor caters to the high-performance requirements of server motherboards, offering more power connectors and delivering greater wattage to support multiple CPUs and additional hardware.

How is the SFF power supply distinct from standard power supply units?

Small Form Factor (SFF) power supplies are distinguishable by their reduced size, which allows them to fit into smaller cases. This design is essential for mini-ITX and other compact builds. They provide the necessary power for the computer while taking up minimal space, which is critical in systems where every millimeter counts.

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