Thank you for your reply!
The Gainward gpu you linked is almost equal to mine, but it's not mine.
This is mine:
https://www.gainward.com/main/vgapro.php?id=1025&tab=ov&lang=enThe only difference seems to be video outputs. All values are the same...
Anyway at the wall gpu is drawing something like 120W instead of 200W shown by miner and GPU-Z.
I know that 200W is crazy for a 2070, but that's basically the power consumption it should have with a 114% Afterburner power limit OC.
Another thing I forgot to mention is that gpu base clock during mining with OC is very volatile. It seems thermal throttling, but temperature is not high (less than 50 Celsius).
In the end I agree with you: I bought this as used and previous owner may have flashed it with a wrong version.
I'll see if I can get some help from Gainward website and facebook page, but I'm afraid that official support does not cover firmware flashing. I hope to find some help among other users, who maybe experienced something similar.
In the worst case I'll keep the card as it is with 114% power limit and 38 MH/s hashrate.