Thank you for stopping by to review my issue. I have laid out the information I have gathered and used to troubleshoot. Please review this and let me know if I am missing something. I believe I have an issue with my 3080. Let me know if you have any questions or suggestions, and thank you ahead of time for your help.
 
System Specifications:
 
PC#1 (Faulted PC)
CPU: Intel i7 10700k
Motherboard: MSI Z490 Unify
GPU: EVGA RTX 3080 FTW3 Ultra
Memory: HyperX Fury 32GB (2x16GB) DDR4 3200 CL16
Storage: 2x(1TB) Samsung 970 EVO Plus NVMe M.2
               1x(2TB) Barracuda HDD
PSU: EVGA SuperNOVA 750W P2
CPU Cooler: Noctua NH-D15 chromax.black
Fans: (Front Intake) 2x140mm Noctua NF-A14 PWM chromax.black
         (Rear Exhaust) 1x120mm Noctua NF-S12A PWM chromax.black
Case: Fractal Meshify C
 
PC#2 (Spare PC)
CPU: Intel i7 4790k
Motherboard: Gigabyte Z97X G1 Gaming
GPU: EVGA GTX 980ti Classified
Memory: GSkill Ripjaws 16GB (2x8GB) DDR3 1866 CL9
Storage: 1x(1TB) Samsung SSD
               1x(512GB) Samsung SSD
               1x(1TB) WD Blue HDD
PSU: Corsair RM750x
CPU Cooler: Corsair H90
Fans: (Front Intake) 2x140 Fractal
         (Rear Exhaust) 1x120 Fractal
Case: Fractal Define S
 
 
Information:
 
Problem:
PC (PC#1) shut down while using SteamVR and will not power back on.
 
Indications:
Motherboard power LED and CMOS reset buttons are lit with PSU rocker in the ON position. They turn off with the rocker in OFF.
 
Troubleshooting:
1. Removed PSU from PC#1 and connected it to PC#2. The only component swapped was the PSU. PC#2 powered up and worked just fine. Seems that the PSU from PC#1 is good.
2. Kept PC#1 PSU in PC#2 and installed the 3080 into PC#2. Attempted to power on with no response. This makes me think the problem is with the 3080.
3. Removed and reseated the 3080 in PC#2, checked power cable connections, and tried to power up. No response.
4. Installed PC#1 PSU back into PC#1. Installed 980ti into PC#1. Powered up with no issue. This again points to the 3080 as the likely issue.
5. Installed 3080 into PC#1 again, verified good card seating and cable connection. Attempted to power up with no response.
 
Additional Information/Backstory:
I received my EVGA RTX 3080 FTW3 Ultra two days ago. I installed it then, and it was working wonderfully up until a couple of hours ago. This morning I was using SteamVR with a Valve Index. When I selected "View Library" within the option menu, my PC shut down instantly and would not power back on.
I have played several hours of games since installing the 3080 with no issue. Fan curves were adjusted and temperatures were stable. This was not the first time SteamVR was used either. Last night I played Star Wars Squadrons in VR for about an hour with zero issues.
 
Edit:
The 3080 was powered with 3 separate 8-pin power cables each time. This was only possible with the EVGA 750P2 due to the amount of available 8-pin ports. The Corsair RM750x only has 2 8-pin ports, so I wasn't able to test it as a power supply to the 3080. The only other thing I could think to test is different 8-pin cables to power the 3080. Interconnected wiring is generally the last expected component to fail in electronics troubleshooting though, at least in my experience. Based on the nature of this failure, it seems like it is the 3080.

Edit 2:
I just contacted EVGA tech support and started the RMA process. Thanks for your help.

rain2_usa
The only info I see missing is if you used 3 separate 8-pin cables to power the 3080 as a test.  If you have tried this, then it sure does look like RMA time.   

Thank you, I forgot to include that info. I did use 3x 8-pin power connectors to power the 3080 each time. The EVGA 750P2 comes with enough 8-pin ports and cables to do that, but the older Corsair RM750x only has 2 8-pin ports. So I wasn't able to test the Corsair PSU on the 3080.

atfrico
What is the minimum requirements of the PSU to run this GPU?
For how long you have the PSU?
Lastly where you got it from?🤔

EVGA Precision X1 Power tool recommends at least a 650w for my system. The 750P2 is enough to run it.

PSU is only about a month old. Just did a new build for the 3080. Also, the PSU powered my old system just fine when tested and it is currently back in the new system and functioning with the 980ti back in there.

The 3080 was purchased from NewEgg.

Sounds like card design issue / psu compatibility ... see this thread  -->>
 
https://forums.evga.com/FTW3-Ultra-Shutting-down-PC-m3114618.aspx
 

I have the exactly same issue with my 3080 xc3 ultra. Did it happen again after you got the replacement?