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ROG ZENITH EXTREME, power problem w 4x2080Ti

Level 7

It seems that I have a PSU problem, but it is unlikely, and I have a feeling that it might be connected to the mobo, which is a ROG ZENITH EXTREME.
I remember that I had to update the mobo bios for the 2080Ti cards, since the earlier versions could not communicate with these RTX cards.

I have to identical linux boxes: same motherboard, processors, and a 1700W high-end PSU.
One has four GTX1080Ti, the other has four RTX2080Ti. results in 1320W and suggests 1600W.

If I run a simulation (protein dynamics, GROMACS software) using 4 GTX1080Ti, everything is fine. If I move these cards to the other box, everything is fine.
(Failure of PSU, motherboard, RAM, or something else is excluded.)

If I run the same simulations using 4 RTX2080Ti card, the cards get fallen from the bus or the linux box reboots. If I limit the power to 200W for the cards using nvidia-smi, the same phenomenon happens. If I limit the power to 100W, there is no problem.

If I power 2x2080Ti cards from PSU of the same computer and 2x2080Ti cards from the PSU of the other computer (on my office desk, with open houses; so there is 2x1700W) then the simulation runs without any problem also with RTX2080Ti cards.

This is somewhat strange, since RTX2080Ti is told to require less power than 1080Ti.

Could it happen that this phenomenon is a motherboard limitation and would work with 2 PSUs, but not with 1 large one? (mobo: ROG ZENITH EXTREME)
Or is it safe to go with a single PSU over 2000W?

Thanks for your help and suggestions,