The answer is the same. New ATX PSU (Seasonic, etc) with adapter. Many Athlon XP era motherboards were using 5v line to power CPU. That's why it's important to have better PSU on such system. That said, modern 400-450W PSU with 30A 5v should suffice for anything, outside of extreme overclocking (liquid nitrogen, etc).

I have Corsair CX450M 450W PSU in my Slot 1 system. CX450M has 110W combined for both 3.3V and 5V rails and max 20A for both. That should be fine for all PII and at least most PIII systems, but it won't be enough for most Atlhons or P4 computers.

Like Serpent Rider wrote, you need at least 30A or more for those. While most 300W PSUs of the era could deliver 30A for "minor" rails, modern PSUs are different and are designed to deliver most of their power to the 12V rail. There are very few if ANY new PSUs on the market that can deliver thise amps on the minor rails in lower end PSUs and for overclocked high end Socket A systems you practically need top of the line PSU. And even if low-end PSUs nominally can deliver 30A, they simply crash when both 3.3V and 5V have heavy loads. Modern PSUs simply are designed for very different systems and loads.

i've seen the 3.3v rail go past ATX spec in the BIOS when using a newer group regulated psu on a p3 board, so a DC-DC unit should be preferable in any case.

Got it. Which Seasonic unit is the one most choose? All the ones I’ve found typically have 14A or 17A for the 5v rail, and the max I found was 20A for an older used model.

Similar question for DC-DC units: Google results showed most people talking about custom or industrial PSUs that only supply 12v and typically have a battery backup built within. I’m not familiar with these or even what’s implied here (very much a noob with electrical stuff), but they do state there are no units that split off into 5v or 3.3v. The point here for me is to avoid custom and purchase new or, at worst, a refurbished reliable PSU from someone else.

Like Serpent Rider wrote, you need at least 30A or more for those.

I didn't wrote that.

but it won't be enough for most Atlhons or P4 computers.

You don't need strong 5v rail on P4.

I feel the sensible option is to get a PSU that reports how much current is actually used. Below you can see my Dual P-III uses just over 18 amps @ +5 so I expect a 17 amp @+5 PSU would be fine for a single P-III system.

The PSU I am using is good for 20 amps @ +5, see https://thermaltake.azureedge.net/pub/media/p … 7fbd038ec81.pdf

The Serpent Rider wrote on 2020-03-18, 13:53:

I didn't wrote that. […]
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Like Serpent Rider wrote, you need at least 30A or more for those.

I didn't wrote that.

but it won't be enough for most Atlhons or P4 computers.

You don't need strong 5v rail on P4.

True for both. I forgot that P4 indeed was pretty light for 5v unlike Athlons.

FSP400-60GHN

Still in production, 23Amps on the 5V rail, 80+Bronze, costs less than 40 Euros.

When running a 1GHz Athlon system the 5V rail was still @ 4.97Volts.

I’m seeing mixed stories online about FSP not being as quality as they once were. Substantiated or no?

Bumping this before committing to a purchase - finally ready to revive one of my rigs. There are no new or NOS FSP400-60GHN available to ship to my area that I can find online, and none of the newly manufactured Seasonic PSUs or competitors seem to have anything close to 30A for minor rails - typically just 14A or 17A. The consensus I've seen some places is that the Seasonic S12III SSR-500GB3 is a good choice. Still only 20A to the minor rails though. This will be powering the PIII 933 rig I have in my sig. Should this work for my setup?

That Seasonic PSU should work just fine for a P3-933, am using a similar rated Antec with my P3-1Ghz.