PSU is usually hard shut off like some one pulled the plug out of the wall.
Over heating is usually, GPU turns off so screen goes black. And fans go 100% to cool it down.

I would wonder about the temps inside the case. Might be worth playing with the side fan off and seeing if it happens just to test. If it helps then I would look at cable management videos and consider higher airflow fans for the case.

Do you have gsync or a max frame rate set?   Some games will have certain loading screens and interface screens with no fps limit and will go up to several thousand FPS running your card at max for a super basic screen.  You should always have something to set a max frame rate.

I've had same issue but with half life alyx. I also have 3090 ftw3 ultra and I7 8700k.

Piggybacking this thread, I'm also having the same issues. EVGA RTX 3090 FTW Ultra and 10900k. I glanced at Precision X just as it crashed while playing League of Legends. 68C. Screen goes black and fans spin up to 100%. Need to hit power button and hard reset. Running a Seasonic 850W Focus plus gold.
 

Have the exact same issue as shiro, it randomly appeared in league and i have the same power supply. My 3090 was a few weeks old, I tested it with an new evga q 850 power supply and card fried. Ypu likely need to RMA.

Jumping in to revive this thread. Was anyone that was experiencing this issue able to fix it?
 
I too am getting the same issue where both my monitors go dark and GPU fans sound like they're at 100% speed. It happened when I was trying to run Dark Souls 3 with OBS running in the background to record gameplay footage using the NVENC encoder. All the intro cutscenes played just fine, but then my screens lost signal right at the start of the tutorial and I had to hard shutdown. Tried it a second time and the same thing happened at the exact same spot.
 
Funny enough, the game runs just fine if I'm not running OBS in the background. I also tested running other games with OBS running in the background and those worked fine as well.
 
I'm running the latest Nvidia driver, version 457.51. Also running the stock bios on the gpu, and I did install Precision X1 and apply the firmware update on the card.

@AgentKaos and @xdarkfulxx - I wanted to post here quickly. I too was having this same issue with an RTX 3090 (Aorus Gigabyte card, not EVGA). Nothing worked for me: updating/re-installing/rolling-back drivers, changing card power settings, using 1 monitor instead of 2.
 
Finally the only thing that has seemed to work for me is a tip I saw on another EVGA forum post (here: ). I downloaded MSI Afterburner and underclocked my card. The person in this post underclocked by 500 MHz. I didn't go that extreme because if that was going to be necessary, I didn't want to lose that much card power. I tried -150 MHz from base clock and memory, and I no longer experience the black screen issue. In Afterburner, I also turned on the MSI power controls.
 
I still plan to contact manufacturer and likely initiate an RMA over the holidays? Why is it necessary to underclock these cards to prevent them from blackscreening?!?! But at least I've found a way to keep it under control for now. Hope this helps.

I've had a similar issue.  Time to RMA the card.
 
https://forums.evga.com/Unusual-problem-with-the-3090-FTW3-Ultra-last-night-m3162616.aspx

QingFengX
try to upate driver

I've tried 4 different driver versions, including the latest game ready driver and had the exact same issue with all of them.

New driver released yesterday. Here's to hoping. Would be nice if EVGA were to address this as an issue.

My replacement 3090 FTW3 Ultra has the same issue with the monitor turning black and the fans spinning up to 100%.  It only happens in DX11 games, but not in DX12 games.  It does the same thing in two different computers using two different monitors.

How could EVGA allow this to pass QC? So many people are having issues yet EVGA just refuse to say anything..

iCue sucks big time, it crashed my Games on multiple systems and my freinds as well. Corsair sell RGB fans that cost a fortune and the software sucks. 

I have had this card for about a week. This just started happening, and had not happened at all the previous week. What I changed. 
 
Moved the card to the lower PCIe slot.
Installed GeForce Software to download the free Call of Duty: Cold War game and updated to most recent drivers via GeForce. I downloaded to original drivers via the EVGA site.
 
What i noticed. The new card placement was over the M.2 Drive, which made it go from an 41 degree temp to over 60 degrees. I was afraid of this because this card run super hot, not necessarily at the GPU but the heat it radiates. However, from i looked up, this was an OK temp.
 
I started playing WOW, and it blacked out and ramped the fans up twice in one day. I read that this happens when it over heats (makes sense). Except, it never happened before. 
 
So I turned off the PC, moved the card back to higher slot (hopefully giving more air flow under the card, and also letting the M.2 drive breathe). Uninstalled all the Geforce software and drivers.
I then re-installed the drivers from the EVGA site. Overall, everything seems to be running cooler. So I think a few things were overheating after awhile. 
But, because i did everything at once, i do not know if it was also due to the software and update as well. 
 
I will see if it does it again, and update. 
 
 
Update: 
I've played WOW, the game that cause this issue, for twice as long and now, no issue. I also played Cyberpunk for awhile and nothing. So it definitely seems to be something to do with overheating. Whether the location of the card or the airflow in the tower. 
I re-arranged fans and RPM profiles. I also flicked the switch on the card from OC to Normal, although I don't know that affects anything on this model or not.