This can be used to test a power supply or allow you to use the power for other electronic circuits.
You need to strip off some of the wire insulation from 4 different wires as shown.
Solder the green wire to a black wire then cover the solder joint with electrical tape.
Solder a power resistor between a red wire and black wire then cover the solder joints with electrical tape.
With the supply plugged in and switch in the on position the power supply will not turn on. When this plug is connected to the main ATX connector the poser supply turns on.