So i built a holw new rig, finally got my hands on an MSI RTX 3080 which kept messing up my system ( Display would not come on_, so i returned it for a RTX EVGA 3090.
FPS are 40 in ultra on my 49 inch wide screen in 1440 P, no problems flying, and everything is butter smooth, but in the SDK, when i start working on a project, the whole system seems to reboot!
Have the newest drivers from Nvidia, monitoring CPU and GPU temps and they dont seem to be a problem.
850 Watt EVGA PSU ( Motherboard requires 350 Watt, the 3090 requires 350 watts also.
I used the EVGA website tool to calculate my PSU requirements and it comes as 702 Watts, so 850 Watts should be enough.
I did install 3 new fans in the case same time as the GPU, but they only take about 7 watts each )
I just cant figure out why my PC reboots! does not happen in other programs, only in the SDK.
Anyone else have this issue ?
My next step will be to update the mobo Bios, and swap out the 3090 back for my humble but trusty 1080 ti and try to isolate it to either the GPU ( making sure its not some other component . (but everything else worked fine when i just had my 1080 ti in there, i could work on the SDK for hours with no issues, maybe occasional CTD but not a reboot of my whole PC
Any ideas ?
set up :
Asus rog Maximums Fomula XII
64 GB DDR4
i9-10850 intel
EVGA RTX 3090 FTW2 Ultra 24 GB.
Try swapping the 1080 ti back in first and see what happens - troubleshooting will (hopefully) be easier if we know whether it’s the GPU or just some crazy coincidental timing.
Never buy a new card until drivers are stable.
i hope its just a driver issue and not an issue with the actual card ( hardware)
Question for the further elimination of the PSU. Don’t the RTX3000 cards have LED’S that signal if there was insufficient power for the card?
90% it is a driver issue, i always wait 4-6 month before buying a new VGA, my first card was a Cirrus logic, then Tseng labs ET4000, 3DFX, Gforce, Radeon etc etc and my experience shouts me, wait wait wait 
Check with other apps and many games before swapping, if it is stable is a driver issue.
If working properly an 850W Psu is enough mate as the minimum required are 750W.
I have the RTX 2080 Ti, on a 850W PSU… And I’m getting the same Reboot issue when flying.
My solution, I underclock my GPU by -300 MHz… much more stable, and no more reboots. and I have 5 case fans installed in my case with good airflow too.
Determining that might be tricky, having not bought that card to test them on.
I bow to your superior knowledge on the elimination process of fault-finding mate. If it says 850W on the PSU, correct arithmetic proves a fault-free condition and PSU efficiency rating is irrelevant. If my PC is running slow, I never check the CPU clock speed because it says 5GHz on the chip. And I never check the screen resolution because I got a 4K monitor.
Now I understand mate.
I think you’re looking too far.
Maybe, but unlikely is not the same as definitely eliminated and not taking five seconds to look at a fault-finding aid LED incorporated by the manufacturer seems a bit silly.
He did not mention about hardware faults, so first look at software then hardware, and i wrote “if the Psu is working properly”
OK I understand now. What you meant was: do not look at the LED as suggested, use a voltmeter and oscilloscope instead. Got it now.
Bye
I did not say that , pls next time read all answers ! Bye 
UPDATE : So yesterday evening i finally got around to updating my Mobo Bios ( Asus Rog Maximus XII) and since then i spent a few hours in the MFS SDK with no Crash/reboot of my PC anymore.
I also set up PRecision X1 and am able to manually check the 3090 to see if it is getting hot ( the RGB LED can be color coded to go redder if it is heating up too). No such problems.
So it seems the BIOS update worked … So far!
Yes there is a red LED that lights up on the corner of the EVGA 3090 if it is underpowered.
In fact it went on the first time i connected because i forgot to connect the third 8 pin connector ( this requires 3 separate 8 pin connector cables running from the power supply. The red LED went on, but not since.
This is a great card though, a true Ferrari of Graphic cards, just the red lips alone are so sexy looking, lol
MODERATOR TRANSLATION:
I also have a 3090, the system freezes when I move an SDK window, more response from MSFS.
I think the power supply is sufficient, I have 750W is OK, I also have 6 fans, cpu 9700K 32GB ram.
j ai moi aussi une 3090, le système se fige quand je déplace une fenêtre du SDK, pus de réponse de MSFS.
Je pense que l’alim est suffisante, moi j’ai 750W c’est OK, j ai aussi 6 ventilateurs, cpu 9700K 32Go ram.