It depends,
Total system wattage is determined by ALL of the components that comprise
it. As a custom computer builder, I don't even think about the Power Supply
requirements until I've settled on what I am building, first. Only then do I
calculate the required watts. However, knowing how big a power supply you
need is only part of the equation. You also need to know the required amps
for the 3.3v, 5v, and +12v lines. The most important one here is the +12v
line. You will find alot of barebone systems with cheap PS's that are rated
at 350 watts that only have 10A-12A on the +12v line. For example, I just
finished building a pc for a customer based on the following:
AMD Athlon XP 2600+
512 Megs of DDR 2700 RAM
DVD-RW drive
DVD/CD-ROM
80 Gig. Hard-Drive
EPOX 8RDA+ Motherboard (With 6 USB ports, Sound, Nic, and Firewire)
128 Meg Geforce FX 5200 Video Card
Floppy Drive
(3) Case Fans
And here are the power requirements:
226.8Watts total
6.9W on the 3.3v line
14.3W on the 5v line
11.05W on the 12v line
Now, the above esitmates are based on a system that is running all
components at 100%. As you may have guessed, this will never happen.
Nevertheless, the values presented should give you some Idea of what is
required. Take a look at the 12v line. Do you think that 350W PS special on
Price Watch with 10A on the 12v rail is going to cut it? I don't think so.
Yeah the max watts are way above that listed in my example, but the 12v line
isn't going to make it.
So, what did I end up using in my customer's computer? Take a look
http://www.newegg.com/app/Showimage...48-17.JPG/11-124-048-14.JPG/11-124-048-19.JPG
If you post your system specs, I will give you an esimate on what you need
for Power.
Hope this helps,
D.