Let me simplify it for you. I could run 3x R9 380 on a 350W PSU if I only used it for light browsing and never mined. If you can't understand that more usage uses more power, then I don't know how to help you.
Hehehehe Wolfo or RobertD , you are so funny, we are speaking about 750W not 350W, and in your case, your miner is pushing R9 380 VGA above 220W, which is VGA "harassment" hehehe. If you don't agree that 220-250W for one R9 380 chip is not to much, in that case you have totally wrong picture mate.
One more time PSU is not a problem, it can be 3K W unit, but VGA consumption is so high above real max manufacturer declaration, which will lead to GPU degradation, and at the end chip death!
OFF and OUT!