I have a 750Gold and I don't know if it will have enough power also. I sure hope you have those power units in stock :P 

I have a 5900x and 3080 FTW3 Ultra. I have been experiencing infrequent shutdowns with my 750 GA (my RMA for a different model is "preparing to ship") since I put the system together last weekend. I'd kept my RAM at 2133 Mhz, but I decided to move it up to 3600, which is what its rated for. My shutdowns increased significantly, and I've moved it back to 2133 Mhz. Its seems to have initially helped increase stability, though I expect to still have shutdowns. I haven't tried underclocking the 3080 to see of that helps.

I know it's not the memory as it passed Memtest86 just this morning.

If you are shopping a new PSU the mini version of the 1000W is cheaper than the 850 Platinum or Titanium, don't know if this is a good idea but will provide headroom.

@tribunal88. I have no doubt you are pushing PSU limits. And yes, xmp or clocking ram higher is a greater power draw. Undervolting GPU should give you more stability if it is indeed a psu issue. I suggest you use a wattage calculator to get a better idea of what you power requirements are. There are probably a number, but seasonic has a good one if you can't find any other. Be sure to set GPU and CPU frequency to max boost level to get a cleared picture of requirements as these can jump quite a bit between idle and boost. I would then use that as an 75%-80% value of the psu wattage you should have. As a rough calculation, I would estimate your setup at around 650-700W (keep in mind the FTW3 Ultra is rated for 450W maxed out). I would say a good quality 850W psu would be the min requirement (more if you want future proofing)

New psu (1300w platinum) fixed the issue for me. 
 
Did a stresstest with OCCT at 110% power limit for 15min without any shutdowns.
 
750w was not enough.
 

arestavo
A shut off/restart indicates that the power supply can't handle it, or the video card is being pushed too high (usually overclocking - I've actually had this happen on my 3090 FTW3).
 
Test in another computer (friends/repair shop), test a different power supply.
 
If you cannot do either, RMA the card. If the problems persist, RMA the power supply.

this

I have a 750-GA that they are RMA-ing to an 850-G+. It will get here sometime next week. I'll post the results here, but based on , I expect it to resolve my issues.
 
I have had some success underclocking my 3080 FTW3 Ultra by -200Mhz when gaming. I also dropped my memory from 3600 to 2133, which seemed to help also. Obviously I don't want to run like this in perpetuity, but its helping me limp along while I wait for the RMA to arrive.

i guess its my power supply too. 3090 ftw3 ultra, rog thor 1200w. random restarts unless i downclock. i took someones alternative of turning on maximum performance in nvidia drivers and now i can overclock without the restarts. guess the psu really couldnt handle the power spikes.

Can someone explain what moving to "Maximum Performance" does. What settings in games are being overridden by the driver?

My PC shuts completely down (have to turn off the PSU by the switch x 10 seconds, then turn it back on) intermittently while gaming.  It's a Thermaltake ToughPower Grand 850 RGB.  I talked with Thermaltake about it, and they want me to RMA the PSU.  I have a Corsair RM1000x coming from Best Buy that will be here on Tuesday.  Hopefully that fixes it.  It doesn't happen often, but when it does, it's only while gaming.
 
EVGA RTX 3090 XC Ultra
AMD 5950x
Trident Neo DDR4 -3600 RGB, 16x2
Asus TUF x570 pro wifi
Sabrent gen 4, 1tb m.2
Sabrent gen 3, 1tb m.2
Arctic Liquid Freezer II 360mm AIO