Question PSU passes paperclip test but doesn't boot 2 mobos

Jan 21, 2021
My Pc has been working fine however today I tried to turn it on and it just wouldn't turn on. I did all the usual tests to see if it was the button or a loose connection but got nowhere, I tried the paperclip test and it passed it. Then I resigned myself to putting in my old working 4 months ago motherboard/cpu/ram, put the 24pin and 8 pin in, no GPU and still nothing, no fans or lights at all.
My gut tells me its the PSU but I don't have a spare or a multimeter to test it.
A 'paperclip' test only tests the PSU's ability to at least power on, and deliver voltages when under no load whatsoever...; it's quite basic, and, is not indicative or conclusive of a 'good' PSU in any way, shape, or fashion.