PSU Form Factor

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PSU Form Factor

These standards define everything from the size and shape of the PSU to its electrical requirements and output. Power supply form factors have been standardized in order to increase compatibility. ATX PS/2 is by far the most popular form factor, and will fit in the vast majority of cases. ATX PS/3 is a compatible with PS/2, but is slightly shorter in depth. ATX PS/3 PSUs are less common and used more in smaller cases such as mATX cases. SFX PSUs are used primarily in small mITX cases since they are smaller than ATX PS/2 PSUs in all dimensions, but adapter brackets can be installed for compatibility with ATX PS/2 cases. Server PSU form factors exist, but are very rarely used in consumer applications. The chart below shows the dimensions for power supply form factors.

There are two major form factor standards that buyers of gaming-grade power supplies might run into, prompting the 'ATX12V vs. ESP12V' question we often get. Here are the differences between ATX12V and EPS12V on power supplies:

ATX12V v1.0-v2.3: The ATX (Advanced Technology eXtended) PSU standards are mostly for desktop PCs and have been maintained by the Intel Corporation. In February of 2000, ATX12V v1.0 was launched, with major updates occurring in February 2003 (v2.0) where the main connector was changed from 20 pin to 24-pin; more updates were seen in March 2007 (v2.3) where the ATX PSU spec was absorbed into a larger document called the "Power Supply Design Guide for Desktop Platform Form Factors, Revision 1.1."

EPS12V v2.1-v2.92: The EPS (Entry-level Power Supply) standard is maintained by the SSI group (Server System Infrastructure). Its current revision is the "EPS12V Power Supply Design Guide, V2.92." The EPS standard is designed for servers where uptime is critical, and as such, the electrical standards and requirements are more stringent due to the higher demands of server computing environments.

What does this mean for me? If you're gaming, you'll see more of ATX12V form factors than EPS due to the type of usage your PSUs will be loaded with.

PSU Form Factor

Width (mm)

Height (mm)

Depth (mm)




140 (or more)








100 (longer is considered SFX-L)

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Author: Michael Kerns

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