Stefan Mileschin

Small Form Factor (SFF) sized PCs have been around for many years and its popularity seems to be growing. Consumers have more choices today than just a few years ago. Be it cases, motherboards, graphics cards, or power supplies, there are more options out there than ever. Some of these systems require smaller than a standard ATX sized power supply. One of the more popular form factors for these systems is named SFX. The SFX dimensions are notably smaller than ATX allowing PSUs to fit in small cases while still delivering adequate power and having appropriate connectivity.

http://www.anandtech.com/show/11773/...power-supplies