I had a very similar (or the same) issue with a 270 I had bought. Apparently it was a Dell card that someone previously had flashed a regular 270 bios on.
My issue was that the card would work fine as long as I didn't install the drivers. If I installed the Radeon drivers it would crash as soon as the driver was loaded into Windows (blue screen boot loop). After flashing the correct Dell bios it worked fine.
Currently my only issue is that the most recent Radeon driver that works with the card is from 2020... for some reason Dell Radeon cards always have a different Device ID than the regular Radeons thus sometimes the official Radeon installer won't pickup the cards (I also have a Dell HD7570 and only the Dell drivers work with that one). I don't mind that much because the card is kind of useless with current games anyway.
edit: my card
edit2:
If you don't know what brand your card is, there's a number just above the PCIe connector that has a format like "109-11236982 C3"
Enter that string on a search engine and see if you can find out.