First, we use the oscilloscope probe's ground wire to connect the power supply's ground, and then use the probe of the oscilloscope probe to connect the voltage under test. The voltage accuracy needs testing when the board is unloaded and fully loaded. AstroAI Digital Multimeter Tester 2000 Counts with DC AC Voltmeter and Ohm Volt Amp Meter; Measures. For anyone looking to diagnose issues with electronic devices, troubleshoot a malfunctioning computer, or simply verify the health of an AC/DC adapter, understanding how to effectively use a multimeter to test a power supply is a fundamental skill. Sumnacon 4 in 1 Banana Plug Alligator Clip Pure Copper Fork Test Lead, 3.