How can I verify the good operation of a power supply with a multimeter?
Computer Doctor: By using a multimeter, you can check the output voltage. For this to work, the power supply must be connected to a load, meaning a motherboard and at least one hard drive. More of a load is better so it’s best to test the supply while fully installed in a system. Use the meter to backprobe the connector terminals and check voltages between the terminals and the chassis ground. All voltages should be within plus or minus 5% of the rated amount. Grounds should register LESS than plus or minus 10 millivolts (thousandths of a volt). To properly verify functionality a power supply manufacturing company uses a load tester which could switch in different load amounts, and also a scope would be used to verify the cleanliness of the signals. Lacking this type of equipment, the best test device a technician can have besides a voltmeter is a “known good” spare. That means a high quality replacement supply you know works, and which can be swapped in place of the suspected bad unit
