Computer Power Supply- Schematic and Operation Theory The diagram below shows a partial schematic of a 450 watt ATX power supply. Its construction is typical for a modern computer PSU with MOSFET switches and active power factor correction (PFC). Note that most schematics circulating on the internet depict old ATX power supply – Circuit Wiring Diagrams ATX power supply provides a 5 V standby voltage, when power is used. This standby power controls a small circuit on the mainboard, also the power switch that connected to the housing. If you push this switch, it triggers the power-on management of the power supply to ground, which will turn the led and power supply turn on .