My question is, the 450W has less amperage on 2 of the big rails. SO how does a 350W PS have more amp than the 450W? http://www.newegg.com/Product/ProductCompare.asp?CompareItemList=N82E16817181102%2CN82E16817704002&SubCategory=58

Yeah, it looks like they have either the rated wattage or the amperage output wrong on the 350 watt. The output wattage is approximately equal to the sum of the various volt x amp products. (Approximately because the output isn't a pure DC wave.) That puts the wattage of the alleged 350 PS at around 480 watts. The same formula for the 450 PS comes to about 455 watts. So unless I'm missing something, the 350 PS figures are wrong.

"Approximately because the output isn't a pure DC wave." DC doesn't produce a wave. Not trying to be a wise guy, could you elaborate on what you mean? Just curious thanks As DAVEINCAPS stated, sounds like a typo to me too.

It's not necessarily a typo. A power supply can be rated at 350W even though the sum of all the volts*amps is greater. What it means is that each voltage has a maximum amperage it can supply but the maximum power you can extract at any time is 350W. So you might have 5V/50A and 12V/20A which gives a total of 490W but on a 350W supply you can take the 50A at 5V but only 8.25A at 12V (or any other combination). As for the "DC wave", there ain't no such thing. The DC is fully stabilised. I think what Dave is trying to say is that the power supply is a switching type, which means that it oscillates at a high frequency in order to reduce the size of the transformer. The waveform generated by the switcher isn't a pure sine wave, but that doesn't matter as it's rectified and stabilised and comes out as pure unvarying DC. Bryan Bryan

I have looked around for tyring to calc the wattage of PS's based on volt/amp ratings on the dc rails. if you do the standard V * A = watts. it never agrees. could you show this calculation?

Here's a clip & below it is the site that I took it from...a lot of good info in the article so it's worth the time to read: "Typically ATX power supplies are rated with a maximum wattage for the +3.3 and +5 line combined meaning that the total of both, no matter the ratio, cannot exceed the designated rating. This is an extremely important number to note when looking at power supplies. A manufacturer may even combine the +3.3, +5 and +12 line and provide a maximum wattage rating but this is not as common." http://www.short-media.com/review.php?r=133 ASUS A7N8X-X Athlon XP 1800+ 8.5 x 200MHz 1024MB PC3200 2.5-3-3-7 Asus A9550GE/TD 128MB WinME/WinXP Pro SP1

...because they are both CHEAP power supplies - spend a little more money and get a better one. Rule #1: Good Computers don't go down. Rule #2: There is no such thing as a good computer.