My rx480 cards can be powered 400W each safely (i even build own modular cables), my rig can work stable till 2,5kW (now using 760W), i am prepared for any algo with overclocking
ummm... dare I say that this seems like a huge waste of headroom? Yes, I understand that it is ideal to have a max load of about 25% less than your PSU's wattage rating, but you indicate that your system has 70% headroom. Not sure how you can ever ROI a system that includes excessive costs from idle PSU wattage capabilities, but you're right lol... you are certainly prepared to max out those 480's
He is probably using a server PSU with an adapter board to break out the connections into a usable configuration. This is actually a pretty typical configuration and the server PSU's can be bought for little to nothing ($20-$50) depending on efficiency and capacity. Running at 240V inputs, a 2,000W-2,900W capacity server PSU is not that uncommon and readily available on places like eBay and Amazon.