So recently (Probably within the last few months) my PC has started suddenly shutting off and then rebooting.  I seem to have tracked it down to GPU issues as my 9800X has run stable in Prime95 at over 300W solid for 45 minutes no issues.  If I play Flight Simulator Tech Alpha though my 2080Ti will be pegged out at almost 370W if not more  according to GPUz and can trigger the shut down almost instantly.    I have had it happen in Star Citizen and Anthem as well during high GPU loads.  It really does seem to be GPU related though.
 
I am in contact with Seasonic right now about possibly swapping out my Ultra Prime 1000W PSU but I was just wondering if the Motherboard could possibly be a culprit here.  I know  they GPU supposedly can pull up to 75W from PCIe Socket and I'm wondering if that could possibly trigger the issue?  I do believe it is the Power Supply but I just was curious if the Motherboard could also be at fault here.

arestavo
I don't know about Anthem, but aren't Star Citizen and MS Flight Sim both CPU heavy? It sounds like the combination of high CPU and GPU on a failing PSU.
 
Try a non-CPU intensive benchmark like Uniengine Valley at as high a resolution and AA as you can set to see if looping that causes a shutdown. 
 
It could also be a recent Windows 10 update. I had a bad one forced on me several months ago that did what you're experiencing. Look in the recently installed section.

I'm running occt 3D stress test right now. It's way overkill obviously. CPU only doesn't matter. I ran prime95 avx2 test for almost an hour and nothing. Running occt and changing the power limit back and forth from 100 to 124 seem to trigger it. And I did a fresh install of Windows 1903 back in oct/nov. The only other update was 1909 which seemed stable enough but I can't remeber if the problem started before or after that update.

"PC has started suddenly shutting off and then rebooting" ---> Classic PSU failure

cletus-cassidy
I'm having the same issue on my X299 Dark with an overclocked 7900X and two 1080 tis, all under water. My rig is pulling 800-950 watts under full load, but I have a brand new Corsair AX1600i, arguably the best PSU out there, so pretty confident that isn't the issue. Could be though I guess.
 
I get reboots in RealBench after 30-45 minutes and also when I run Heaven + Prime95 together ("homemade" RealBench to stress whole system). AIDA64 Extreme stress tests crash (not a reboot) when I run CPU + FPU + Cache + RAM + GPU. It doesn't crash when I run any of these individually. It also runs fine on 3DMark.
 
Is it possible we are tripping some power limit on the X299 Dark? Alternatively, should I try a new PSU even though this is one of the best and brand new?

No issues at stock clocks?

cletus-cassidy
I'm having the same issue on my X299 Dark with an overclocked 7900X and two 1080 tis, all under water. My rig is pulling 800-950 watts under full load, but I have a brand new Corsair AX1600i, arguably the best PSU out there, so pretty confident that isn't the issue. Could be though I guess.
 
I get reboots in RealBench after 30-45 minutes and also when I run Heaven + Prime95 together ("homemade" RealBench to stress whole system). AIDA64 Extreme stress tests crash (not a reboot) when I run CPU + FPU + Cache + RAM + GPU. It doesn't crash when I run any of these individually. It also runs fine on 3DMark.
 
Is it possible we are tripping some power limit on the X299 Dark? Alternatively, should I try a new PSU even though this is one of the best and brand new?

"...I have a brand new Corsair AX1600i, arguably the best PSU out there..."


Typically with power issues I would exepect to see the system FAIL shortly after the PSU is fully loaded, not 30 to 45 minutes into a benchmark. That being said I would not be too quick to dismiss the power supply the AXi series is known to have problems as seen with the reviews for the more frequently purchased AX1200i, https://www.newegg.com/corsair-axi-series-ax1200i-1200w/p/N82E16817139039. Not saying for sure that it is the power supply, but certainly could be a possibility. 
 
That being said assuming that its not the PSU it certainly could just be that the CPU is not stable with your current OC and as @Sajin suggested I would see what happens at stock settings. Also keep an eye on temperatures the fact that it FAILS after 30 to 45 minutes of benching would suggest an overheating issue.
 
Side Note: SeaSonic makes by far the best power supply's and not to sound like a fan boy, but I would take an EVGA power supply over a Corsair any day. =)   

jasoncodispoti
@Sajin did my post get removed? 

Yep. Restored.

jasoncodispoti
@cletus-cassidy, thinking about this some more... For giggles go into the Corsair Link software and disable multi-rail mode, setup so that its operating with a single rail. Test again and see what happens... 
 
@Sajin, thanks! 
 

Multi rail mode is definitely a possibility. 
 
No problem.