PC building woes

I recently bought a new processor, motherboard, RAM and CPU cooler to upgrade my computer. Here’s the list of specific parts:

Intel Core i9-12900K 5.2 GHz
Asus ROG STRIX Z690-F GAMING WIFI
G.Skill Trident Z5 RGB DDR5 6000MHz 32GB 2x16GB CL40
Noctua NH-D15 chromax.black

The RAM sticks pass the built-in MemTest64, the processor withstands the Cinebench test, but when I tried to use my VR headset, the computer shut off. I downloaded 3DMark, suspecting there was a problem with the GPU (a GeForce RTX 2080 Ti that has been working fine for about a year). I finally removed the daisy chain configuration, that I couldn’t be bothered to change, to connect a second PCIe cable, but 3DMark keeps shutting down the computer randomly.

Some Google searches have suggested that the PSU might be faulty. I’ve been using this PSU for about six years. It’s an Aerocool Templarius Imperator 850W. I calculated online whether the combination of new parts would require more power than what my PSU provides, but the calculation suggested I’d need about 630W.

So what might be the issue here? I’m considering the following:

1. Best case scenario, I’ve missed a drivers issue with the new Windows installation, although I have installed the latest nVidia drivers.

2. Might my GPU be at fault? Is there a way to test its components in isolation the same way MemTest86 or Cinebench do for the RAM and processor respectively?

3. Maybe my PSU has always been faulty, but I’ve only found that out now that the new processor, motherboard and RAM, added to the GPU, are stressing it more.

If I have to replace the PSU, I don’t look forward to dismantling half of my tower to remove the current one; it might be the hardest part to remove from my Dark Base Pro 900 tower once it’s installed.

I know I won’t rest easy until I solve this problem, so I’m scouring online forums to figure out if I’ll have to buy a new PSU and dismantle half of my setup, as I fear.