Hello everyone.
I sincerely ask for help from the community.
Currently I have two PCs mining Zcash/ETH (depends on their market price). Nothing is overclocked. RX 470 have modded bios.
First one is: Mobo p8h61-m le, CPU i5-2300, 8 Gb RAM, HDD 160 GB, 3x ASUS Strix 470 4 GB,750W PSU (80 Bronze).
The second is pretty much the same Mobo (except it has 4 PCI-e slots), i3 CPU, 4 GB ram, HDD 80 GB, 1x Asus 380 4 GB, 600W PSU (80 Bronze).

So I intended to switch PSU, as I checked that each RX 470 has TDP=120 Watt, so that means 120*3=360, leaves about 200+ Watt for Mobo, CPU and HDD. Should be enough. So I switched, but the farm worked for like 2-3 minutes, then PSU turned itself off.
My plan was to use 600W PSU on the MB with 3x470, and use 750W with 4x470 (remove 380 completely).
But now I am a bit confused: I am afraid that if 3x470 don't start on 600W, I believe that even 800-850W PSU (I intended to buy 800W for rigs with 4x470) won't be enough for 4x470.

Again, I don't overvolt/overclock anything, only using modded bios cards.

Do you have any ideas/suggestions on what PSU should be used with 4x470? Should I not try to save money and buy 1000W PSU already for 4x470?

Really looking forward to any ideas. Thanks!