The following two articles detail why!
The first link shows how to calculate the size. The next link is why I add 100 to that total.
PS. Not to mention that power supplies age so you need more Watts that you calculated to get a machine that will run well for more than a year.
Hi. I'm going to be building a custom computer in a few months, built for gaming (mainly RPGs and RTS's, so I don't need anything too fancy), and all the other normal computer tasks. I was thinking about getting these parts, and I was wondering what people think about them, or anything I should change. This is my first time building a computer, so help would be appreciated. Here's what I'm thinking:
Case: DYNAPOWER ATX Black Mid-Tower Case with 430W Power Supply, Model D58-BK
Motherboard: Intel D865PERL i865PE Chipset
Processor: Intel Pentium 4/ 2.26 GHz 533MHz FSB, 512K Cache - Retail
Memory: Crucial 184 Pin 512MB DDR PC-3200 8T - OEM
Video Card: NVIDIA FX 5500 256MB AGP
Floppy Drive: NEC 1.44MB Black Internal Floppy Drive, OEM
CD-ROM Drive: Samsung Black 52X CD-ROM, Model SH-152AEBUB, OEM
Hard Drive: SAMSUNG 80GB 7200RPM IDE Hard Drive, Model SP0802N, OEM Drive
Wireless Adaptor: NETGEAR MA111
The Nvidia Geforce FX 5500 requires 250W minimum power supply. In total, I tallied it up, and the whole computer requires 335W supply. My uncle (who's very good with computers, and has built many many ones) said that I should have 50% more power supply than I need, just in case, which would mean I need to take out the 430W supply and put in a 500W or 550W. Is this necessary?