got my first rig coming online. 6x Sapphire R9-390. I have 2x 750w power supply. Am I good? Does anyone have these cards and know the watt draw? Thank you :-)
My 2 x Gigabye R9 390X + motherboard, CPU, drive + fans consume ~ 700 watts (measured with a power meter at the wall) - see Is CPU mining even worth the Ether? . My GPUs are only slightly overclocked.
Your 390 and my 390X have a 275 watts thermal design power (TDP) - see http://www.pcper.com/reviews/Graphics-Cards/Sapphire-Nitro-Radeon-R9-390-8GB-Review .
I have a 850 watt 80+ Gold (see https://en.wikipedia.org/wiki/80_Plus) power supply - this has sufficient power to support 2 390X GPUs and the other components.
Your 750 watt power supplies may have enough juice to power 2 of your cards. Better to err on the side of caution and add a margin by using higher wattage power supplies.
Also note that AMD motherboards/CPUs consume more power than the eqivalent Intel motherboard/CPUs.