Desktop computer power supplies provide two or more low-voltage, high-current, isolated power rails,typically a 5V rail and a 12V rail. More an more often, it also provides a 3.3V auxiliary rail with high-current capability.The power is generated by an off-line forward switching converter (inside the so-called "silver box") that regulates only one power rail through an isolated feedback loop. The other power rails are usually postregulated to meet the specifications on the output voltage tolerance and regulation. A typical architecture is shown in fig. 1.