ATX PS/2

• This is by far the most popular PSU form factor and is often called the “standard ATX PSU”
• Standard dimension for this form factor is: 150mm (W) x 86mm (H) x 140mm (D)
• PSU with depth longer than 140mm can still be considered as an ATX PS/2 model

ATX PS/3

• This form factor is compatible with ATX PS/2, the only difference is the shorter depth.
• Many have also called this the “Micro ATX” PSU form factor, which is incorrect as no such standard exists for power supplies.
• Standard dimension for this form factor is: 150mm (W) x 86mm (H) x 100mm (D)
• The depth for this form factor may vary from 100mm up to 139mm

SFX

• This form factor is popular with small computer cases and is also often wrongly referred to as “Micro ATX” power supplies. Because this standard is smaller than ATX PS/2 in all dimensions, it can be used in cases that support ATX PS/2 with simple adapters or brackets. Some retail SFX power supplies are sold with adapters included
• Standard dimension for this form factor is: 125mm (W) x 63.5mm (H) x 100mm (D)
• There are variations for this form factor that have longer depth such as SFX-L, a term created by SilverStone in 2014 in conjunction with SX500-LG’s announcement.

SFX-L

• Description: A “long” version of the SFX form factor that provides more power and cooling capacity in a small package.
• Dimensions: It is longer than a standard SFX PSU but has the same width and height.
• Features: Fits in cases that are too small for ATX but need more power and better cooling than a standard SFX PSU can provide

Flex ATX

• This form factor is often used in small computer cases and is sometimes wrongly referred to as “Mini-ITX” PSU
• Standard dimension for this form factor is: 81.5mm (W) x 40.5mm (H) x 150mm (D)
• There are variations for this form factor that have longer depth.

TFX

• This form factor is commonly used in computer cases with limited height or non-standard shapes.  It has similar proportions to Flex ATX but is bigger in all dimensions.
• Standard dimension for this form factor is: 85mm (W) x 65mm (H) x 175mm (D)
• There are models with varying depth, but usually shorter than 175mm

PS/2 Mini Redundant

• This form factor has similar dimension to ATX PS/2, but because it requires hot-swap capability, the mounting holes to computer cases are different.  Usually cases designed to fit PS/2 mini redundant PSUs have separate bracket to support ATX PS/2 as well
• Standard dimension for this form factor is: 150mm (W) x 85mm (H) x 200mm (D)
• There are models with varying depth, usually around 200mm

Resources

• https://www.silverstonetek.com/en/tech-talk/10055