Question Was it possibly my power supply?

[Satearn]

My PC did something weird yesterday.

When I tried to start it, this is what happened:

• The screen had lines as if broken and it was stuck on AsRock start screen
• Turned it off, then no beep on reboot, just blank
• Kept trying to turn it off and on, but blank screen, no start beep, and little LED light not flashing as usual, just blank

So I tried this:

• Disconnected power supply
• Connected and old power supply
• Tried to start the PC, didn't start
• Reconnected power supply
• Then PC worked again and now using it to type this!.....

What could have been the issue?

 

[Aeacus]

Full system specs, including PSU make and model (or part number) is? Also, how old the PSU is, and was the PSU bought new or used/refurbished?