Hi I'm building my own PC and I require a suitable power supply. The spec is:

Pentium 4 @ 3.0Ghz
GeForce Nvidia 6600GT
1 CD-DVD burner
2x hard drives
a few usb devices
1 PCI card for video capture

I think this will require no less than 350W. A local shop has no 400W units but they do have a 500W unit on special offer (cheaper than the 350W they stock). I was hoping to get a 400W unit. Will it be OK to use a 500W unit even if it's full potential is not required? Will it overload my motherboard????

400W or more would probably be a good thing for this build.

The important factor in power supplies is actually the power they provide to the internal components, not the maximum power they consume - which is how PSU Wattages are rated.

A PSU provides a number of important rails to the system; +12V, +5V and +3.3V. Each rail has an ampare rating, that represents the maximum power it can provide. PSUs of the same Watt rating will differ in ampage for each rail on the efficiency (read "quality") of the unit. On a decent 400W PSU, you might see 18A on +12, and 20A on +5 and +3.3. An extremely cheap 500W PSU might only provide 15W on +12, and 17W on +5 and +3.3. It all depends.

Usually, people go by a sort of average expectation when talking about PSUs by wattage. Anyone who is looking seriously will pay attention to the actual power output.

Cheers Syph,

I'm not quite following. When talking about 400W you say "you might see 18A..... and 20A...." then when you talk about 500W you say it "might only provide 15W......". Is your unit of measurment in A or W (it changed) ?



I see that you mean there is more to it than just how many WATTs it says it provides on the box/case of the PSU. However I don't know much on the subject so when you refer to +5 and +3.3 I'm not sure what you are trying to say. Thanks anyway though.

Ah yeah sorry, 15W was supposed to be 15A.

It's not really important that you understand which devices use the +12, +5 or +3.3 rails, just that you understand that more power permits the use of more or higher drain devices. Some PSUs even have multiple +12 rails (this is often the most heavily used). Be aware that a single 25A +12 is inferior to two 18A +12s for example.

Basically, I'm saying that if a high wattage PSU is cheap, it's probably because it's inefficient.