I'm planning to put myself a new system together which should consist of the following components:
* CPU: Intel Core2 Duo E8400
* MoBo: Gigabyte GA-EP45-DS4 (P45)
* RAM: 4096MB Corsair PC2-800 CL4 TWIN2X4096-6400C4DHX
* Graphics: ATi Radeon HD4870
* HD: most probably a 3.5" Seagate ES.2 500GB with 32MB cache
My question is now, what kind of power supply do I need? Would 650W be enough?
More than enough. Usally when you use stronger PSU than needed the system will always run just the PSU needs more energy for itself - that means when you choose the best match then the energy consumption is a bit lower, but in your case I don't think this aspect really matters *g*