Amazon has EVGA SuperNOVA G2 850 watt gold-rated power supplies on sale right now for $91. These are very highly-rated efficient units, and a good choice if you’re looking to build a mining rig composed of 3-4 RX 470 GPUs (PSUs are most efficient when delivering roughly half of their rated maximum power, which puts this unit in the sweet spot for a 3-4 GPU rig).

While this unit is technically capable of powering 6x undervolted RX 470 cards, you’ll be running it near its maximum capacity, which will hurt its effective efficiency quite a bit. I still strongly recommend a 1200+ watt PSU for 6 GPU rigs.