Judging only by the size of heatsinks and transformers, I'd say you'll be lucky if that thing does even half the ratings on the label.

From the other options you mention, the PCP&C Silencer 750 could be a good option assuming it's in good condition.

I just undervolt my athlon xp to get headroom with a modern psu. Don't know how well the original athlon is undervolted though.

I definitely wouldn't use the PSU in your photos. If you open a PSU and the PCB looks like a ghost town and the transformers are small... I would just move on. Glad to hear you have some other candidates lying around.

Hey, thanks for the advice. I don't usually open psus so I didn't really have anything to compare it to. I ended up pulling the ibm one, opened it up and put them side by side https://imgur.com/a/IOU15Ce. The ibm is only rated for 330watts. I think I'll use this one for solder/desolder practice, at least it will be good for something. BTW, good call on the silencer. Its rated for 30amps on the 5v and 24 on the 3.3v. 170watts max for both the 5v and 3.3v. That sounds like enough for the Athlon build, right?

cxm717 wrote:

Hey, thanks for the advice. I don't usually open psus so I didn't really have anything to compare it to. I ended up pulling the ibm one, opened it up and put them side by side https://imgur.com/a/IOU15Ce. The ibm is only rated for 330watts. I think I'll use this one for solder/desolder practice, at least it will be good for something. BTW, good call on the silencer. Its rated for 30amps on the 5v and 24 on the 3.3v. 170watts max for both the 5v and 3.3v. That sounds like enough for the Athlon build, right?

Great lesson/comparison in PSU quality. What the sticker says is rarely the whole story. That IBM PSU is obviously the better device.

Also, don't get too fixated on high Wattages. An Athlon Thunderbird 1400C uses max 73W, so that's about 15A on the 5V line, and the AGP slot can draw max 2A from the 5V line. Allow a very generous 5A more for the rest of the system and you hit an absolute peak of 22A, unless you are doing some very heavy stuff on the PCI bus. A single PCI card may draw up to 25W (5A) from the 5V line, but system designers are not required to budget for maximum simultaneous load on all slots at the same time. In practice the PCI bus won't draw much over 5A total. In any event you saw more than enough SoA systems being shipped with 250W PSUs (in fact some OEMs dropped as low as 200W, but very 5V-heavy ones).

You only need monster >30A 5V PSUs if you have dual SoA systems, as you're looking at over 26A just for the CPUs there (worst-case, with Palomino Athlon MPs; Tbreds and Bartons use slightly less). But with a modern PSU, getting those 25-30A on the 5V line may need a rather heavier PSU than if you use a period one designed to deliver most of its power on the 5V line. As for which is better (old PSU with fat 5V line vs new PSU with high Wattage and huge 12V capabilities being unsused), that is a lively discussion, but both work fine if they're quality PSUs. Bottom line is you want to go for the best quality PSU you have, and looking at that photograph it's pretty clear which one that is 😉

That first supply is quite the horror show. I suspect the ground point isn't even compliant.

The VRM regulators for the CPU are not 100% efficient. Assuming a conservative 80% efficiency, the 75W you quoted to the CPU will likely require 90W to the regulators.

What's the power distribution breakdown of the IBM PSU? There should be a label that gives output amps for the 12V, 5V, and minor supply rails.

Its rated for 30amps on the 5v and 24 on the 3.3v. 170watts max for both the 5v and 3.3v.

90W is still only 18A, taking the whole 22A net and adding 25% overhead still is only 27.5W, so well within the margins of those 30A. Also he has an Athlon 1200 max, not 1400, so its peak draw is going to be lower.

Here is the ibm psus label https://imgur.com/a/garZYcY. I think the ibm system this came from had 2 300MHz p2s in it

That's your PSU, for sure. The power distribution is appropriate for anything you might want, and Acbel is a solid OEM.