PSU/consumption question...

[Achilleslastand]

For example if my cpu uses 125 watts and my gpu 150 watts what else needs power and how much?

[Crazyeyesreaper]

125 and 150 is expected never 100% true but roughly

an HDD at spinup aka boot can draw up to 20-25w
Fans can draw .5-5w each
Motherboard draws power to feed PCIe / PCI / cards other then the GPU,
RAM 15-30w depending on Speed Capacity etc
Optical Drive 5-10w

pretty much only CPU and GPU matter for typical power consumption figures, unless running 3-4 sata hdds or multiple add on cards etc

[Jaketh]

In most cases unless your running SLI or high end single GPU cards a 500w PSU will be fine.