certain psu models have worse issues with the voltage spikes of the 30xx series cards than others do,... but a safe bet for your card is at least a solid make 1000W 
  Gold rated minimum , preferable platinum or Titanium
 

thanks

however this power meter is definitely under calculated, it recommends 750w psu wich is definitely not enough

Kay_nyc
however this power meter is definitely under calculated, it recommends 750w psu wich is definitely not enough

depends on many things .... looking at the minimum PSU is never a good idea for OC maximum

Kay_nyc
I am using an evga 3080ti ftw3, 11700k, 32g gskill ram, rog z590 strix mother board. The PSU that I choose is corsair RM850, however I often met with the system rebooting while playing high quality games like red dead 2 and cyberpunk 2077, which is frustrating. however it never reboots when I do ordinary works like office work or watching YouTube, so I think it's the PSU's problem of now enough wattage? Could you guys give me some advice on this?

Probably.  How old is the PSU?  Daisy chain splitter cables to the GPU?

my present psu is new. and what's the second question asking?

Kay_nyc
my present psu is new. and what's the second question asking?

Do you have three individual cables from the PSU to the GPU.  Or do some of them have two connectors on the GPU end with a "daisy chain" wire?  And if so how are they plugged?
 
For example in the pic below, THIS IS BAD for a 3080 Ti FTW3:
 

 
 
#1 plug is front of machine (left), #3 is back of machine (right), #2 is middle.  #1 and #2 combined on an out of the box 3080 Ti FTW3 can pull nearly 300w, which is bad if they are on the same cable.

Cool GTX
 agree with kevinc313 using separate 8-pin cables is best practic
 
Ck your PSU Mfg for their recommendation is another option
 
 
GPU-Z sensor tab will tell you how much power the GPU is pulling on each 8-pin & total
 
Make sure your not putting too much load on any one part of PSU ... check PSU specs .... Amps per section/ type of Voltage ... not just total Watts

Three cables or at least daisy chain #1 and #3, don't go over 100% power.

Kay_nyc
I am using 3 separate 8 pin cables, still got the problem

Can you describe the shutdown/reboot in more detail?  Is it like someone just pulled the power plug out of the wall?  Or is it like the screen goes black, everything else (lights, sound) continues for a few seconds, then it shuts off and restarts?  Or is there a BSOD?  Or is there a freeze up of what is on screen then restart?

Bummer.  Sounds like a protection circuit on the PSU or GPU is being tripped, likely the PSU.  Is the PSU definitely an RM850, not an RM850X?  The RM850X has been widely recommended as OK for a 3080 Ti FTW3.  Not sure about the current version of the RM850.
 
You might be able to RMA the PSU, maybe they can upgrade you to a RM850X.  Or you might want to upgrade to a good 1000w unit.  I like the Superflower Leadex SE 1000w Platinum when it's on sale for ~$180 or less, or the EVGA version 1000w P2.

1000w