I mean even my craptastic VS550 Orange could handle RX 480, GTX 470 in period of 6 months, yes 12V rail dropped on 11.6-11.7V with GTX 470, but with RX 480 it was 11.8V~ , I would suggest him to try, if he feels the stuttering, clock drops, then I would consider swapping PSU, but most of time everybody and me Including (By everybody i mean most of us here) would yell "New PSU".
But that's his risk as well as my risk When i used GTX 470 in my system, but It worked out fine. No buzzing, no burning smell or nothing.
I would suggest him to try out.
Oh and to add, I have this PSU for 4-5 years all-ready (Im quite unsure), 2 years out of warranty.