[SOLVED] PC random restarts, kernel 41, trying to nail down the problematic part.

[Dukesilver27-]

Hi, my PC is about 10 months old, all parts except GPU was brand new.
Specs:
i5-12400
ASUS Prime B660M-A D4 WIFI
Team Delta TUF 2x8GB 3200 CL16
Team MP33 1TB
ASUS TUF RX 6800 XT OC
MSI MPG A850GF.

Issue description:
PC randomly restarts, sometimes even when idling it restarts, it gets progressively worse over time. Over the span of 3 days time, it went from once a day to every few minutes.
Event viewer said Kernel 41 after every crash, so I assume this is hardware problem.

What I've done:
1. Update drivers and windows.
2. Tried running it iGPU only.
3. Tried running without any USB devices plugged except for standard office keyboard and mouse.
4. Re-plugging all PSU cables, even swapping the cables to the backup ones that came with the PSU.
5. Bought a PSU tester, tested the PSU, according to the readings from it and online guidelines, voltages and "PG" are all within range of tolerance.
6. Disassembled everything and tried running it on a test bench style (without case).
7. Disabled XMP, running only with 1 RAM, swapped RAM, changed RAM slots.

Last development:
I run the PC with only iGPU and let it idle for about 2 hours, no crash whatsoever, then I decided to stress test with Cinebench, it compeleted the first round of 10 min run, but crashed during the second 10 min run.
Then I tried running with GPU, tried to stress test with Diablo 4, crashed within minutes after the game entered the character selection screen.

So, this leads me to think that either the PSU or the motherboard is at fault.
My question is, which is it? I'm looking for opinions from experienced builders/troubleshooters. Thanks in advance.

Just additional information, ever since I first build this PC, the metallic parts of the case and USB devices with metallic parts sometimes shock me. If this matters, the wall plugs in my country are all 2 prongs (type C), which means they are not grounded, socket is also type C but unsure whether it is grounded or not (old building).

 

[Dark Lord of Tech]

I'm leaning towards PSU.

 

[DaleH]

I'm leaning towards PSU.

Me too.

 

[Dukesilver27-]

I'm leaning towards PSU.

I frankly have never done any RMA because this is the first hardware issue I've had since my first build about 8 years ago.
Do you think this falls under warranty coverage for a PSU?

 

[Dark Lord of Tech]

Do you think this falls under warranty coverage for a PSU?......Yes you can RMA it.

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[Dukesilver27-]

For whoever finds this post, I fixed this issue by swapping out the motherboard.
After doing the steps above mentioned by me, you either need to go to a PC repair store or shell out money for a part replacement without actually knowing which one is broken.
In my case, it was either the motherboard or CPU because I had no way of confirming.
Based on the symptoms I encountered, I deduced it was motherboard issue, the symptoms were:
1. Random shutdowns
2. Unable to POST, occasionally it does POST but very rarely
3. Minor physical damage either caused by failure or inflicted by yourself.

Tests I did before deducing motherboard failure:
1. Reverse all software and drivers update done that week. (BIOS was updated at least 5 months ago)
2. Complete disassembly, re-plugged every cable.
3. Booting with only 1 RAM (tried both sticks and on every slot), without GPU, without SSD/HDD, without RAM, tried a new stick of RAM, clear CMOS.
4. Re-seat CPU and CPU cooler.
5. Did the same as step 3 but I put it on the motherboard box, test benching it.
6. Swapping every PSU cable with their spares that come with the PSU. Swapping the PSU power cable, and also different power outlets.
7. Sent PSU for RMA.