Question Mysterious power cycling on new build ?

[C4ke]

Components are as follows:
-Asus TUF 3070ti GPU
-(8x4)32GB 3200mhz Corsair RAM
-1000w CorsairX PSU
-11700k Intel CPU
-Asus Z490-E Motherboard

So I recently upgraded my wife's PC that now mysteriously power cycles under load. It boots up fine, can enter a video game(WoW, Stray, C2077), but then power cycles after being under load for a minute or two. This never happened when she had a EVGA 1660S, but started when I swapped it for a 3070ti. As soon as I put in the 3070ti, the PC started to power cycle under heavy load in the x16 PCIE slot. In the 8x slot, it rarely power cycles. Undervolting does not solve this issue. Now, anyone would think that immediately the GPU is DOA right? Wrong. I tested it in my own PC and it worked, even under heavy loads for an extended period of time. Overclocked just fine too, which is something it cannot do in her PC without crashing. I even tested her PSU in my PC with my components(11900k and 3090) and the PSU worked. Memtest86 shows all good with her RAM plugged in to my PC.

I have reassembled her PC from scratch to ensure that everything is properly inserted. The BIOS is updated, and I even tried flashing the mobo because I am out of troubleshooting ideas. I am beginning to think that it is possible that the motherboard is faulty. I guess it could be the CPU as well, but I doubt it as that CPU has been overclocked for months without any sort of failure. I have already tried undoing all overclocks and the issue still persists. I have triple checked to make sure every single possible plug is filled, including the 8-4 pin CPU on the motherboard. I have monitored temps under load, and they are within expected ranges. No crazy power spikes either that I can see, the crash just seems to happen randomly "under load". There is no artifacting during crashes. Windows has also been reinstalled fresh with new drivers.

To further explain the "power cycle": The screen immediately goes black, the RGB patterns on the PC case freeze, and then reboots normally with no error displayed, almost like it is not getting enough power somewhere as I have experienced a similar crash before with my 3090 at first and a insufficient PSU. I am at a loss. What could it possibly be? Please shoot me some ideas, speculations, anything to try.

 

[Ralston18]

Use Task Manager and Resource Monitor to observe system performance when the power cycling occurs.

Use both tools but only one tool at a time.

Determine what resources are being used, to what extent ( %), and what is using any given resource.

Hopefully you will spot some pattern in what is taking place or a particular culprit when the power cycling occurs.

Process explorer may also prove helpful. Microsoft, free:

https://docs.microsoft.com/en-us/sysinternals/downloads/process-explorer

Just take your time observing. It may take a bit of time and effort to understand and navigate within the tools. Do not immediately react to anything that appears astray. Do some additional research and then, as applicable and appropriate, make a change as warranted.

Change only one thing at a time and keep notes in case you need to undo some change.

And, as you should always be doing anyway, ensure that all important data is backed up at least 2 x to other locations. Verify that the backups are recoverable and readable.