kalm_traveler wrote on 2021-04-25, 16:16:

Hey guys, I searched around a little bit to see if we already had a thread of recommended modern power supplies for these old pl […]
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Hey guys, I searched around a little bit to see if we already had a thread of recommended modern power supplies for these old platforms but didn't come up with anything.

I understand that pre-Pentium 4 era, load was mainly on the +5v rail vs the shift to almost entirely on the +12v rail that we have now days which means that lower wattage modern PSUs are often not able to push enough amps on the +5v rail to properly run Pentium III and older systems.

That being said, I finally made up my mind on parts for my 98SE/2k rig and have it more or less buttoned up save for not having the final PSU sorted out. I'd purchased some old very high-watt PSUs to recap a couple years ago but didn't understand capacitor ratings properly so after replacing all the big caps on them they wouldn't turn on.

Currently, I have an old ~ 2004ish no-name PSU with 40A on the +5v rail that seems to boot and run this PIII rig but I don't trust it being so old, not recapped and a no-name brand. I also have a new EVGA 550w modular unit but it only has 20A on the +5v rail and with all PCI cards installed it won't turn the board on.

I watched a youtube video from I think Phil's Computer Lab some time ago where he mentioned this issue, and poking around I see that Corsair PSU's have a few more amps on their +5v rails when you step up into the really high watt supplies like the HX1200 has 30A on +5v but honestly 1000w and higher PSU's seem to all be snapped up by crypto miners these days so I'm not even sure I could find one of those if I wanted to justify the expense in the first place.

Are there any known new-ish other PSUs that should work for this?

For reference, this rig is built on:
an Asus TUSL2-C motherboard
PIII 1.13ghz Tualatin chip
3 sticks of PC-133 SDRAM (256mb, 128mb, 128mb)
AGP Quadro4 980XGL graphics card
Intel 1gbit NIC
USB 2.0 card
SATA card
Aureal Vortex 2 sound card
USB 3.0 card in PCI-E to PCI adapter (works under Win 2k, albeit not at full speed due to PCI bus limitations, still faster than USB 2.0)
IDE DVD-RW drive
floppy drive emulator

Ideally also have 4 case fans (12v fans) run by a Corsair fan controller.

All I can tell right now is if I remove some of the expansion cards, the 550w EVGA PSU will boot it up but with everything installed it seems to not have enough amps on that +5v rail as the machine won't turn on at all. With the old no-name PSU it boots up and seems to run more or less fine.

Any suggestions on modern PSUs I can look for, or are those expensive high-wattage Corsair units probably the only option?

You can get away with using a DC to DC conversion PSU that generates the minor rails from the main 12V supply. They don't suffer from the same cross loading issues as group regulated designs. Unfortunately, you're going to have to pay for a relatively powerful unit for a P3 system (one that can supply around 20A should do). Athlon 32 bit systems usually need more (unless they have on motherboard 12V conversion).

The Startech ATXPower series was pretty much the last ATX12V 1.3 compliant PSU out there and it seems to be NOS only now, sometimes listed for absolutely shocking prices. DC-DC conversion and the used market appear to be your two remaining options.