So I did try swapping PSU and while the blackscreen did stop, now the PC is shutting down after intense use. Either I have 2 broken PSUS (which were working fine with a GTX 970) or this GPU is killing them.
How have you connected your card to your monitor or tv i.e via hdmi, dvi, display port etc? have you tried using different cables? the power supply is fine. The card needs minimum of 500w.