I upgraded my 12100f to a 12900kf and since then I'm experiencing random shutdowns under load, underclocking my cpu and turning off hyperthreading has resolved the issue somewhat, but is not a permanent solution as I may as well have kept the old cpu if I'm doing that.

I'm thinking the issue could me my PSU, but I'd like some advice first.

Build is

i9-12900k
rtx 3080
4x8gb DDR4 - 3600mhz (XMP enabled)
ASUS Prime z690-PLUS D4
Thermalright 360 AIO cooler
850W PSU

I've tried turning off XMP, new thermal compound, then a ThermalGrizzly Graphene sheet, thinking it may be an overheating issue. I've been in BIOS and tried performance vs extreme settings in the AI Tweaker.

I don't particularly know what all the BIOS settings do, so I don't fuck about with them too much, but I turned off HyperThreading and Turbo mode, which stabilised the PC, but ruined the playability of some games, weirdly directx12 stopped working when I did this, but works when I have everything default, until the CPU is under high load then it shuts down.

I've had all the fans on max and it still doesn't help.

Could this just be that my old 850 isn't good enough for the more power hungry card? I've seen a 1000w PSU that isn't too expensive, but is enough that I'd rather not buy it if it's not going to fix the issue.

I've also lowered the max cpu usage to 98% but this still wasn't good enough for stability.

Any ideas? Or just buy the PSU and eliminate that possibility?