Question PC power/boot issues

[d3nny]

Over a year ago I built a PC with the following specs:

• Motherboard: MSI PRO Z690-A DDR4
• PSU: Corsair RM 750x
• CPU: Intel i9 12900k
• GPU: Nvidia RTX 3080
• RAM: 48GB DDR4
  

It worked perfectly until a month ago when it abruptly powered off while idle and would not turn back on. There were no lights or signs of activity from the motherboard.

I took it to a repair shop and they found the PSU had "blocked" itself as a protective measure due to an electrical issue. I also noticed melted plastic on my power cable, so I replaced both the power cable and extension cord.

Everything seemed fine for about a month until yesterday. When attempting to turn on the PC, it failed to power on again. I checked motherboard to see if there is any lights turned on and saw that the Ethernet port showed power. After unplugging and waiting a few hours, it magically turned on.

Today, I faced the same issue, but after repeatedly pressing the power button, it eventually started.

Is my PSU faulty?
Does anyone have ideas on how to further troubleshoot or confirm if the PSU is defective?
Or what else could potentially be the culprit here?

 

[punkncat]

Pls explain 'extension cord'.

Melted plastic on the power cable would seem to indicate to me that you are using too thin wire for the extension cord.

 

[d3nny]

Pls explain 'extension cord'.

Melted plastic on the power cable would seem to indicate to me that you are using too thin wire for the extension cord.

Extension cord is this:

My original power cord (for PSU) was meant to be used in UK and I am in EU.
UK and EU have different power outlets, so I was using an adapter for my power cord.
Adapter was a bit melted, so I threw it away and bought new power cord, which is compatible for my (EU) outlet.

Currently I am using new extension cord and new power cord.