How to Check Power Supply Voltage

Connect your multimeter probes to your multimeter and turn it on. Observe the correct polarity. The red probe is the positive one, and it is plugged into the red plug on the multimeter. The black probe is the negative or common probe, and is plugged into the black plug on the multimeter.

Set your multimeter function to measure either an alternating current (AC) or direct current (DC) voltage, depending on the output of your power supply. Most power supplies for commercial use produce a DC voltage.

Turn on the power supply. Make sure it is plugged into the appropriate power source. Most power supplies operate by plugging into a typical 120 house circuit.

Connect the multimeter probes to the power supply output terminals by touching the probes to the metal contacts. Power supply outputs are usually marked with a positive (+) sign and a negative (-) sign. Observe the correct polarity with your probes by touching the red probe to the positive terminal and the black probe to the negative terminal.

Read the multimeter display for the output voltage of the power supply.