Did you buy the PC as a prebuilt or build it yourself?
I got an Alphasync 3090 prebuilt in December 2020, the PC is amazing but for some reason instead of using two cables from the power supply they chose to use just a single cable with a little splitter that plugged into the other GPU slot, so all the power was coming through a single cable.
Here’s a pic of the joke splitter to show what I mean;
It kept shutting down all the time. Plugging in another cable so that the card was getting the proper amount of power to it fixed it completely and it hasn’t crashed since.
Regarding temps, when you say 90 degrees, what part of the temps are you referring to? GPUz will give you your GPU temp, your VRAM temp and your Hot Spot temp. 90 for a hot spot under load would be very low, mine use to get up to 106 before I undervolted. 90 for GPU would be high, mine stays in the 70’s, with VRAM a bit higher. The hotspot is a pain though as it’s the hottest part on your card, and often thermal paste isn’t optimally applied so you could a cool card overall but there is a single hotspot due to inadequate thermal paste application that causes your fans to sound like a plane taking off and the card to throttle.
It’s worse with the 3090 than the 3080 and 3080Ti becuase of the 24 GB of VRAM but it could also be what’s causing yours to heat up.
Here’s a screen shot showing what mean, note my PC is currently idle, the temps get a lot hotter under load, but I think the GPU is low 70’s, VRAM high 70’s, and the hotspot will touch 100 then the fans kick in.
