You wouldn’t use a typical SFX power supply for something where size matters; you’d likely use a Flex PSU, which are often long and thin. If you got a lower-power CPU with integrated graphics, you could manage a case that’s not much bigger than the motherboard or much thicker than the IO shroud.

Lemmy doesn’t have a lot of SFF or Ultra SFF content yet, but getting the most out of limited space is definitely a thing people are into, and they can get quite creative.

The final product is often portable but still rarely as tiny as a mini PC or NUC-like. Depending on your needs, someone might be better off making a Steam Brick.