You did notice they used a 980 Ti, which will yield better FPS than the RX 480 as long as the CPU bottleneck is not 100%?

I think I posted this in some other thread already, but here you can see how an OC'd FX-6300 bottlenecks an RX 480 compared to an OC'd i7-6700K:
Even though the FX-6300 keeps both the RX 480 and 980 Ti from achieving their full potential, the 980 Ti can still give significantly better FPS than the RX 480 when paired with the FX-6300.
At least Sapphire states that the recommended minimum power output is 500W for the reference models. AIB models will likely have even higher recommendations due to overclocking and the fact that the stock reference model draws 164 W according to Tom's Hardware. Of course there will be some headroom in those recommendations, so one might easily get away with an even smaller PSU, depending on the rest of the parts.