OK, after recently ording & receiving two PSUs, I'm finding that my knowledge of PSUs is somewhat lacking. See the following posts: http://www.computing.net/hardware/wwwboard/forum/21824.html http://www.computing.net/hardware/wwwboard/forum/22195.html As I understand it, the +3.3v rail is primarily for the motherboard, & the +5v rail is for the drives. The +12v rail was more for fans & wasn't considered quite as important, but now that the P4 & some videocards require a 12v connection, the +12v rail has become as important as the other two rails. Is this essentially correct? Anyone have any links regarding PSU ratings, how to choose a PSU, what the different rails are used for, etc? Thanks.

The cpu runs off the 12v rail, but only after the mobo has converted it down to 1.5v or whatever. The fans plus the motors of the cd drive and hard drives run off the 12v rail The circuitry of the hard drive and cd drive run off the 5v rail The mobo uses the 3.3v, 5v, and 12v rail. Note that aside from the drives and fans, most power comes through the mobo, which is why the mobo's voltage regulation and conversion circuits are key. The abit nf7-s has held top overclocking spot among nf2 boards for a while, one reason being that it happens to have the best voltage delivery subsystem. When you have a power problem sometimes you have a motherboard power problem not a psu problem. Here is a good thread on psus... http://www.community.tomshardware.com/forum/showflat.m?Cat=&Board=comp_power&Number=357&page=0&view=collapsed&sb=5&part=all&vc=1 and a good article http://www6.tomshardware.com/howto/20040122/index.html --------------- The power supply is the only component that destroys other components, and is also the most insidious to troubleshoot when its dodgy. So you'd think a basic rule of thumb would be "don't skimp on the psu". Well the problem with that rule is that no psu brand other than PC Power & Cooling differentiates itself in practice from the others. So my own rule of thumb is to by one with a higher rating than I need (like 400w-450w), and get a mid-tier brand like fortron. Another good strategy is to buy a psu that gets high marks from quiet pc enthusiasts: http://www.silentpcreview.com/modules.php?op=modload&name=Sections&file=index&req=viewarticle&artid=28&page=2 because any psu that performs well while being quiet is one that needs little airflow to cool it which means it converts power efficiently without producing much heat, which probably means its high quality.

I wouldnt say that any one of the power rails is more important than the other. Any one fails and the computer stops working. The power supply is designed so that if the 12V rail fails, so does the 3.3v and 5V rail. This primary to protect the memory because if the memory gets 3.3v and no 12V current is will be destroyed. The following links will give you some idea. http://www.pcguide.com/ref/power/sup/spec.htm http://www.intel.com/design/motherbd/atx.htm The PDF documents from Intel contains a wealth of information. Stuart

Thanks guys, I'll look into the links you posted. I realize I bought a cheap unit...although I've read good things about CoolMax, I have no idea about this Hercules unit. Did you happen to check the specs that I posted? From what I've read, they tend to be misleading anyway, but it's seems the CoolMax is the better choice?

The hercules goes for $15 on pricewatch, the coolmax for $36. I think they are screwing you by giving you the hercules - its the cheapest 400w psu made I think. That coolmax looks like a good unit.

Jam, Wasn't it you that watched a volt meter register 16+v when a psu failed in front of your eyes? That's a good thing to avoid. Skip

Skip, Yea, that was me! That was when I tried to push my 1.33 Athlon Tbird up to 1.54 (11.0 x 140). It seemed to be running stable, but when I ran Toast, the 12v rail spiked after about a minute & the system shutdown. I was watching my monitoring program when it happened & I thought the whole thing was "toast"...lol! It's still running with the same PSU though, I just backed it off to 1.47 (10.5 x 140) & it's been stable for months. When I saw the CoolMax unit at Str8buy for only $8, I figured "what have I got to lose?"...then they "substituted" the Hercules units instead. I fired off an e-mail & am waiting for a response.