Power Supply Form Factors and Sizes Explained

Power supply units are a crucial part of any gaming PC; however, they are often neglected due to being ostensibly boring. Despite this, there are some important things to be aware of when shopping for a new power supply, and one of them is the subject of this page: PSU Form Factors and sizes.

Wattage and efficiency are not the only things to be considered when you’re in the market for a new PSU, you must also make sure you’re getting one that adheres to the correct form factor. Luckily, PSU sizes are governed by standards, so the lessons you’ll learn here are applicable even if you pick an inferior brand instead of CORSAIR.

ATX (Advanced Technology Extended) is responsible for this standard. You might recognize it as this is also the body in charge of motherboard sizes and, indeed, what goes on inside your power supply (but that’s considerably more complex and a subject for another time).

The rub here is that there are three main form factors that your power supply can take: ATX and SFX / SFX-L. Interestingly, the regular ATX standard designates the width and the height of the PSU, but the length can vary. But for the SFX and SFX-L standards, the length is set.

This is because most PC cases that call for regular ATX PSUs tend to have quite a bit of clearance behind the PSU (especially since the HDDs that used to occupy this space have become almost extinct), so the length doesn’t matter as much. But SFX and SFX-L PSUs are used in cases that can get really small, so the clearance matters way more, hence the length restriction.

Despite there not really being a "maximum" length for the regular ATX size PSUs, the length tends to increase in regular increments, hence the multiple lengths in the table above. Examples of ATX PSUs from CORSAIR include the HXi, RMe, RMx, and RMx SHIFT power supplies. (The RMx SHIFT PSUs feature side-mounted cables, but are still ATX-compliant.)

The SFX standard is significantly smaller in every dimension compared to ATX. It is the smallest standard consumer size, so if you're using a very small SFF (Small Form Factor) case, you'll need an SFX PSU, such as the SF850. However, if your case can accommodate a slightly longer PSU, the SFX-L standard typically allows for a higher wattage.

The SFX-L standard retains the width and height of an SFX PSU but increases the length by 30mm. This extension allows for higher wattages while remaining far more compact than a regular ATX PSU. Our SF1000L had to use the SFX-L standard so we could make it 1000W.