Dear Members and Moderators,
(sorry for my english)
I understand that this problem replied many times, but I couldn’t find any useful solution. I want to say, that I’m not professional user, but I want to collect perfect, fast and stable (!!!) home machine – and I spend a really lot of money for this.
My situation:
I bought brand-new card (topic) and plugged it in instead another – RX5700XT (MSI MECH OC). After that I just installed new NVidia drivers (didn’t remove old Radeon drivers) and started to test – play some favorite games – RDR2 and Assassin’s Creed Odyssey. It looked great: more smooth, fast, more details (it’s able to set up more graphic settings), etc. It’s all like I expected.
But after several runs, after some time (10-20 minutes) games started to crash! Monitor just turned off and whole PC becomes silent, it has to be hard reseted. Next times I turned on GPU information in Assassin’s Creed ([F1]) and saw temperature is about 52-56 grads and load is about 85-92% after several minutes of playing, that’s normal! That’s much more colder and less loaded than my previous card that could heat up to 82-83 grads under 100% load.
So situation repeated every time that it becomes unable to play because I don’t know when it appears again (I’m already lost of some achievements in ACO and broke scenario and can’t get forward)…
And I went to internet to find out a solution, and I understood that my problem is not rarely.
What could I find:
1)      Use DDU under Safe Mode to remove old drivers. I did it – same thing.
2)      Use DDU under Safe Mode for current drivers and reinstall. I did it – same thing.
3)      Use DDU under Safe Mode for current drivers, unplug LAN cable and reinstall new drivers w/o Windows. I did it – same thing.
[all of it I made several times]
4)      Check PSU and use separated cables to power graphic card. I think that my configuration is very modern (and very expensive), main components:
MB - ASUS ROG Crosshair VIII Hero (Wi-Fi)
CPU – AMD 2700X (BOX), 4200MHz
Memory – G.Skill F4-3200C14D-32GFX (set-up stable 3200MHz with AMD DRAM Calculator)
Case – Cougar Conquer Black (open-type case with good ventilation) + Phantek Vertical GPU Adapter
HDD – WD Black SN750 (1Tb)
PSU – be quiet! Straight Power 11 850W
Monitor – ACER VG271U (27” 2.5K 144Hz) + DisplayPort v1.4 cable
…
So I think that PSU (and also another components) is in range to use with this card.
5)      Set “Power management mode” to “Prefer maximum performance” in NVidia Control Panel. Done!
6)      Set limit (lock) voltage to 1.2V in MSI Afterburner (and apply settings). Done! But every time it still disappear.
After all of this tries situation became a little bit better: I can play a little longer, but it still is very unstable, all time I have to play with GPU information and wait when parameters becomes higher. It’s very uncomfortable. With my previous card, that as I said is more hotter, I didn’t feel and can’t remember such problems. I just wanted to get something better in performance, but now I’m a little confused with my choice (old card is still with me, I safe it as reserve).
Please explain what is the problem? Why I bought the card, that costs 3 times expensive than Radeon, behaves so unstable? What should I do be calm with my situation without to try it in another rig (I have no where I can do it), without Windows reinstalling (I’m just not sure that it can help, because I read some topics where people tried all of this and still have such problems)? Maybe there is an universal solution “how to set up right setting after you bought 2080 Ti”?
Thank you.

Sajin
#1 Make sure your motherboard bios is up to date. 
#2 Make sure your cpu isn't overheating.
#3 What happens when you set the core & memory to max negative clocks inside msi afterburner?
#4 Could be a psu issue. Trying a different psu is an option.
#5 Since you can't test the card in another pc, or take the card to a local shop for testing you'll need to rma it as there could be something wrong with it, and it needs to be checked out in another computer to verify if it's the problem or not. 

Hello Sajin,
As you took my attention on CPU temp, as I didn't watch for before, I tuned this parameter in RivaTuner to watch online within tests (I use 3DMark - Firestrike, extreme settings), and I saw, that CPU temp is up to 80 grads and more!!! And I think there is a reason when PC goes to turn off! My CPU frequency was tuned a little overclocked - up to 4200MHz in BIOS. Now I changed it to defaults (Auto) and temp became lower on 10 grads.
I think new card is using more CPU than previous card...
So I need much better CPU cooler instead stock one.
I will test more and be in touch!
 
Thank you.