Well, I cut off the metal plates instead, so there is nothingpushing against its fan anymore, but the fan still runs at only 649rpm.
I know for sure that it has ran at around 850rpm before, when I pushed it upwards. This is getting annoying, I guess there is something wrong with the PSU. I'll look around for some info on this particular PSU, and see if the fan still only runs at around 649 rpm if I dont fasten it with screws at all.
The fan control was fixed when I used another connector instead.
Btw, thanks for the tips.
