Simply turn on your power supply, plug in your 20-pin power supply connector to mini-tester and check the LED lights. If a power output is working, the LED will light and you will hear a beep. If the power output fails, the LED will be off with no beep. The Power Supply Tester gives voltage readings for each line. As an added feature, you can also test other connections, such as your floppy drive and peripherals.