Is 400W power supply needed?

you may want to post this in power supplies an cases section to get a better response. it would depend on the brand of the 300W and 400W power supplies, but i'm guessing they are the same brand. if they are a poor quality brand, you may want to get no supply with the case and purchase a quality one seperately.

second is how much power are you goint to need. more is always better, but if cost is an issue, then you may want to figure out if you need the extra 100W: <A HREF="http://www.jscustompcs.com/power_supply/" target="_new">power supply wattage calculator</A>.

I'll go a little further than the others- you almost certainly want a GOOD 400W PSU if you intend to keep this case for a few years and have a fairly modern system (or might upgrade to a modern processor). Why all the qualification to the answer? Because new CPU's, like the P4EE will use up 100W all by themselves. Not only that, but think of the heat put off by a 100W light bulb and you have a very clear idea why newer systems want lots of cooling fans. BUT, even those fans eat up power.

A rule of thumb: There is no such thing as TOO MUCH power supply!