Trying not to knee jerk at that image and say "Burn it with fire!!!", so real talk now, the R7 TDP is workable on a 300W PSU. Tom's own benchmarks imply total system load, under load, around the 150w mark (http://www.tomshardware.com/reviews/radeon-r7-240-and-250,3717-9.html).
HOWEVER, 'Burn it...