I also use corsair btw, HX520
yes, there's a lot possibility
looking at the specs, probably your friend using lot's of cooling device for his computer
while its not directly affecting whole system, but fluctuation might effecting some onboard device (Soundcard, LAN Card, etc), for some device it's not really critical, but for Network device, a single RTO means DC for the game.
it's been a while since I'm using LAN, you can test it by purchasing a cheap PCI Lan card, or WIFI USB/PCI (I'm using TP-LINK WN712n, USB probably the safest bet since fluctuation also affecting PCI Bus voltage)
if DC syndrom still exist, I believe it's the Internet.
Edit: I just realized Corsair provide 5years warranty, if your friend not sattisfied/in doubt he can also RMA it.