The PSU needs to be sized to handle the max startup/surge load. My rig doesn't have a high-end video card which can be power hungry (when they are being actively used), here are the complete specs:
Asus P7P55D-E MB, Intel i7 860, 4GB DDR3 , ATI 4600 Radeon, OCZ-VERTEX 30GB SSD (Boot), WDC...