Optiplex 980 FF How to test power supply

Try a bist of psu.

https://www.dell.com/support/kbdoc/en-us/000125179/how-to-run-a-power-supply-unit-self-test-on-a-dell-desktop-or-all-in-one-computer

If the system won’t power on at all, the PSU is indeed a prime suspect, especially since it tripped your UPS. A couple of things you can try before RMA’ing it under warranty:

1. Basic power reset – Disconnect AC cable, hold the power button for ~30 seconds, then plug it back in and try again. Sometimes the board gets stuck in a protection state.

2. Check the power supply’s built-in diagnostic LED – On most OptiPlex units, there’s a small green LED on the PSU itself. If it doesn’t light up when plugged into the wall, the PSU is likely dead.

3. Paperclip test (if you’re comfortable) – Disconnect the PSU from the motherboard, then short the green wire to any black ground wire on the 24-pin connector. If the fan doesn’t spin up, the PSU has failed. Do this carefully and only if you’re familiar with handling electronics safely.

4. Minimal boot – Remove all peripherals, drives, and RAM, then try powering on with just the PSU + motherboard. If still dead → PSU or motherboard.

Since you just bought it and it has warranty, I’d strongly suggest contacting the seller for a replacement PSU or full system exchange rather than spending too much time testing. Given that it tripped your UPS, I’d lean toward a faulty PSU.

Good luck!!!!

@surijack2610​ Thank you for the advice.  I contacted the seller and they are sending me a replacement.