ATX vs SFX vs SFX-L: PC Power Supply Form Factors Explained

Building a PC starts with selecting a processor. The second critical stage is selecting a compatible motherboard with the right power supply that fits inside your PC case. PC power supply companies understand that users may require varying dimensions of PSUs to fit their PC cases. Therefore, they have created three major form factors: ATX, SFX, and SFX-L. There are some challenges associated with changing the form factor of a PSU while ensuring the same power delivery. It may involve miniaturization of components, which adds to the cost. In the case of heat transfer, smaller fans require higher RPM, which can contribute to PC noise.

This article will discuss these nuances related to form factors and explain their applicability along with technical aspects. By the end of the article, our readers will have a clear idea of which PSU is ideal for their usage scenario. Let's start with the basics on who controls the form factors and standardizes them. 

Who Controls Power Supply Unit (PSU) Form Factors 

Intel as Primary Standardizer of PSU Form Factors

Intel has been at the forefront of PSU standardization. They developed the ATX (Advanced Technology eXtended) in 1995. Since then, they have continued to improve their design, the latest being ATX 3.1. They are also responsible for the development of other compact standards, which include:

● SFX (Small Form Factor): Created for compact mini-ITX builds.

● TFX (Thin Form Factor): Designed for ultra-slim desktops.

● FlexATX: Used in unconventional or slender cases 

Manufacturers Creating De Facto Standards

In some cases, manufacturers release their own designs which are modifications of the standard. However, the market follows them as a trend and adopts them as an unofficial de facto standard.

● SFX-L: Not an official form factor by Intel. SilverStone introduced it in 2014. It just increased the length of Intel's standard by 30 mm to make it quieter. It has since been widely adopted across the industry — ESGAMING includes it as a standard option in its product range. 

What Do These PSU Form Factors Dictate

Manufacturers are required to adhere to stringent standards set out by Intel or the SSI in their power supply unit (PSU) design guides to guarantee interoperability among various PC components. As per the rules: 

● Physical Dimensions: PSU must have precise specifications (Width × Height × Depth) in order to fit into a matching PC case.

● Mounting Points: Where the screw holes are located precisely.

● Cables: The various kinds of cables needed, such as the 24-pin connection for motherboards or PCIe connectors for graphics processing units.

● Electrical Features: For example, "Power Good" indication and voltage stability. 

ATX (Advanced Technology eXtended)

Dimensions: 150 mm (W) × 86 mm (H) × 140 mm+ (D)

For most mid-tower, full-tower, and standard micro-ATX desktop chassis, the ATX PSU form factor is ideal. The PSU's width and height are strictly controlled by Intel's standards, while the depth remains variable. For entry-level PSUs, it can be 140 mm, while the high-end enthusiast builds may have a 200 mm depth. Therefore, any user purchasing should observe the relevant PSU depth and check its compatibility with the PC case before purchase. Owing to its large dimensions, it can accommodate larger fans, thus making it the quietest option in the bunch.

Pros:

● Cooling: Massive 140 mm fans

● Noise: Silent under heavy load

● Longevity: Cooler parts last longer

● Installation: Easy in standard cases

● Replacement: Universally available everywhere

● Aesthetics: Fills large cases perfectly 

Cons:

● Space: Massive physical case footprint

● Installation: Impossible in compact builds

SFX (Small Form Factor)

Dimensions: 125 mm (W) × 63.5 mm (H) × 100 mm (D)

SFX, as the name suggests, is suitable for compact builds. These are often the go-to choice for users who utilize a mini-ITX motherboard with tight internal PC case dimensions. Their most suitable application is a sandwich-style or console-style SFF chassis. Typically, they are used in sub-10-liter enclosures. Depth at SFX is usually controlled. Its 100 mm limits the fan dimensions to be 92 mm. It can cause the fans to spin at higher RPM, thus resulting in noticeably higher noise profile. 

Pros:

● Space: Unrivaled ultra-compact footprint

● Installation: Short cables reduce clutter

● Aesthetics: Ideal for minimalist builds 

Cons:

● Cooling: Runs hotter under load

● Noise: Small fans whine loudly

● Longevity: Thermal stress degrades parts

● Replacement: Expensive, harder to find 

SFX-L (Small Form Factor - Lengthened)

Dimensions: 125 mm (W) × 63.5 mm (H) × 130 mm (D)

The SFX-L format was developed by SilverStone and then taken up as a standard by other industrial giants. These are a slight modification of the SFX design with depth extending 30 mm. It is just enough to allow the installation of a 120 mm fan. It massively changes the acoustic performance of the PSU and eliminates the bottleneck in thermal performance of the PSU. However, there is a drawback of limited cable routing area behind the PSU. 

Pros:

● Cooling: Fits quieter 120 mm fans

● Noise: Much quieter than SFX

● Longevity: Better airflow extends lifespan 

Cons:

● Space: Awkward middle-ground sizing

● Installation: Extra depth crushes cables

● Replacement: Rarest standard on market

Table of Comparison Between ATX, SFX, and SFX-L

Conclusion

There are many form factors available for PSU but ATX, SFX, and SFX-L are the most popular. It is mainly due to their balance of performance and dimensional compatibility. ATX stands as the oldest of the bunch and performs the best for all criteria except space. They are the ideal form factor for professional gamers and creators. In comparison, SFX and SFX-L focus on space efficiency but compromise on other factors.

For PC builders, the key is to find the ideal dimensions for their PC case. It should fulfill their dimensional and power supply requirements. Smaller form factors often come with limited wattage and efficiency. When they do offer high efficiency, they typically carry a hefty price tag and generate more noise. ATX is the ideal choice for the best performance-to-price ratio. Irrespective of form factor, always look for a reliable PSU supplier that offers standardized 80 PLUS certified PSUs. To find the best value for money, consider ESGAMING PSUs - they offer premium aesthetics with modern features, and achieve the perfect integration of product performance, appearance design and installation adaptability.

For more information, visit www.esgamingpc.com