Can I run 2 powercolor PCS+ R9 290 off a 750 watt power supply. http://pcpartpicker.com/part/evga-power-supply-120pg0750gr This is my build LINK
Not with that card... 1000w for 2 in crossfire
If you use crossfire, the power supply might struggle to keep up and you might surpass your power supply's maximum capabilities.
My tip: Stick with one card if crossfire is not necessary immediately and wait for a future upgrade, or swap out the power supply to at least an 850w.
Always allow around 150W of headroom (for load and OC) when using Nvidia GPUs, add about 50W for each additional card in SLI (in addition to the card's base TDP).
If using AMD, you may need up to 300W (for load and OC) when using Radeon GPUs, add about 75W for each additional card in crossfire (in addition to the card's base TDP).
Not only are AMD cards much more power-hungry, their power draw also scales poorly with load and OC compared to Nvidia...in my experience in the industry.
If you have the PSU for it, I'd go with AMD since they seem to have the $-to-Performance edge.
300w for AMD cards? Where do you get your numbers?
That's only TDP, it says nothing about power supply headroom.
150-200w of headroom is the most anyone will ever need.
(headroom is for extreme loading and benching situations)