Count up the total number of pci-e 6 or 8 pin power connectors that your graphics configuration needs.
Get a psu with that number of leads. All your other parts are normal, and accounted for.
A quality PSU will be able to deliver enough power for all the leads at any load and temperature.
Quality units come from Corsair, PC P&C, Seasonic, Antec to name a few.
Your requirements will be satisfied typically by a 750w unit.