Could you please tell me if I can I run 2 x ASUS R9280X-DC2T-3GD5 Radeon R9 280X Videocards on a CORSAIR TX Series CMPSU-650TX 650W PSU.
I really can not get a new supply right now.
I doubt it. You could boot and browse the web just fine with it, but as soon as you put stress on the GPU's you simply won't have enough watts, and i don't think it's good for your PSU at all.