Only way to know for sure is to replace it and test. If error goes away, then that was the issue ( assuming 2 components are not faulty at the same time …)
Or need someone who can diagnose psu directly and test.
Call the repair guy, since you get the error quickly, maybe he can diagnose it better this time.
Another option is to buy new psu and if that wasnt the problem, sell old psu on forum but you will lose some money this way. Or keep old one as backup.
You can google for the error you get in OCCT just in case its helpful. “occt power test crash”
OCCT/comments/o6p3p8/pc_immediately_shuts_down_on_power_test
You can try to reduce clocks / voltages / set power limits and see if that works.
Maybe stress test only cpu and not gpu, does it work ? Then stress test only gpu etc.
Also make sure you dont have overclocks as he said.
Have to rule things out one by one. So probably not RAM and not UPS for now.