motherboard – Is My Power-Supply Faulty? or Could It be something Else

So I Suspect my Power Supply to be faulty but I am unsure and want some advice,

I turned off my PC(full shutdown via windows)
and then in the morning it would not start again, I press the Power Button and nothing happened,(the Mobo indicator lights worked etc.)

So I did the basic Troubleshooting stuff, reaseated everything , checked all connections , tried diffrent power cable and outlets, But still nothing

So I pulled the Power Supply out of another PC , and connected it to my PC and it started up no problem(I cant use that PSU permanently because it is only 400 watts and does not have the 8 pins I need for my GPU etc)

Then I knew everything “worked” so I Jumped-started my PSU and it started,
Plugged everything back into the PC and nothing the PC did not start, did the basic troubleshooting again, still nothing

JumpStarted the PSU again and tested a few pins with a MultiMeter eveything seemed fine
Plugged evrything back and BOOM the PC boots and works fine now

So Could this be the PSU that is starting to give the Ghost? or could it be something else

I am sure it is unlikely that the cables were not connected properly because I checked the connections 6 times