Oh man, I totally feel u on this. I literally spent months reviving a T-Bird build and ran into the exact same wall. Most modern units are basically useless for Athlon XP boards cuz they're all about that 12V rail, while the socket A era is *hungry* for the 5V and 3.3V lines. If you use a modern group-regulated PSU, you're gonna get nasty voltage swings that could legit fry your legacy components... so be careful!!

I would suggest looking for the StarTech 300W ATX12V 2.01 Power Supply - ATX2POWER300. It's kinda old-school but it actually has a decent 5V rail (around 20A-30A usually) which is what those old AMD chips crave. Another solid bet if you can find one is the SeaSonic SS-300FS 300W ATX Power Supply, which was a tank back in the day and still holds up for retro builds.

But honestly? The real pro move now is using the Athena Power AP-P4ATX60FE 600W ATX12V Power Supply. It's one of the few "modern-ish" units that still specifically balances the rails for legacy hardware. Just make sure to check the labels; you want at least 25A on that 5V rail to stay safe. Also, if you run out of Molex, just grab some high-quality StarTech 4-Pin Molex Power Y-Splitter Cable adapters. Just dont overload a single daisy chain or it'll get spicy lol. Good luck with the build tho, those Athlon XPs are legendary!! 👍

Sooo, just found this thread and I totally get the struggle. Finding a modern PSU that doesn't choke on a Socket A board is seriously tough since everything now is all about the 12V rail.

Check out the "JonnyGURU" archives if you can find them—honestly, that site was the bible for power distribution specs back in the day. You might also find this useful: there's a great resource at the Vogons forums called the "PSU guide for retro hunters" which lists specific legacy-friendly units. I'm pretty sure some older Seasonic or FSP units still have decent 5V/3.3V combined wattage, but IIRC, you really want something with at least 25-30A on that 5V rail for a thirsty Athlon XP. Ngl, I've spent hours cross-referencing old PDF manuals just to be sure. It's a bit of a rabbit hole but definitely worth it to avoid frying ur board! gl with the build!!

Seconding the recommendation above! Socket A builds are literally a nightmare for modern rails. Before u buy anything, what's ur actual budget? Also, are u planning to overclock that Athlon or just keep it stock? lol

TL;DR: Avoid modern "Group Regulated" budget units; they'll literally cook your legacy parts because the 5V rail drops too low under Athlon XP loads.

In my experience, you've gotta be super careful here. Most new PSUs are all about the 12V rail, but Socket A boards pull almost everything from the 5V line. If you use a modern unit that isn't DC-to-DC, the voltage cross-loading can get dangerous... honestly, I've seen it fry old VRMs. I've tried many setups over the years, and your best bet is actually looking for industrial brands like StarTech or even some Seasonic industrial units that still spec for high 5V/3.3V amperage. Also, definitely check the labels! You want at least 25A-30A on that 5V rail if you're running a high-end Athlon. It's a wierd power balance to find now, but staying safe with a high-quality DC-to-DC unit is the way to go so you dont kill your retro gear. gl!