MattRocks wrote on 2026-04-11, 11:57:

Luckily, I have an original ATX PSU from the AT/ATX transition era. I was putting that ATX PSU into an AT case by simply remapping the reset button to ATX power button. But, I'm glitched - the world is upside down! The ATX PSU doesn't actually fit the AT case because the inside intake vents that should face-off to the CPU are facing-off to the top of the case.

I haven't heard about this before, but now I'm surprised too.

Luckily, there are still plenty of ATX PSUs with 80mm fan on the bargain.

If you need ATX PSU with 120mm fan and an inverted mounts, you'll probably find it in branded computers (IBM/Lenovo, HP, etc.). There's a similar confusion there - the PSU mounts is upside down.

ott wrote on 2026-04-11, 15:09:

Luckily, there are still plenty of ATX PSUs with 80mm fan on the bargain.

If they need servicing, they aren't a bargain - I had one blow up with a bang.

In either case, mine is an 80mm ATX PSU. Photo attached, showing the ATX assumption is the inverse of AT reality.

MattRocks wrote on 2026-04-11, 16:06:

ott wrote on 2026-04-11, 15:09:

Luckily, there are still plenty of ATX PSUs with 80mm fan on the bargain.

If they need servicing, they aren't a bargain - I had one blow up with a bang.

In either case, mine is an 80mm ATX PSU. Photo attached, showing the ATX assumption is the inverse of AT reality.

Plenty of room for that fan to breathe tho.
And don't forget that in early ATX the PSU-fans were supposed to do double duty, both cooling the PSU and the CPU.
The AT "standard" is basically the opposite of ATX, AT cpu's were (usually) placed at the air intake of the case while ATX had it placed near the PSU to allow OEM's to cheap out on fans =)

Intel Socket 7 (AT era) seems to consistently position the CPU above the PCI slots, which is closer to Intel ATX thinking - only place for the heat to go is up.

AT's only free space for an extra fan is the front intake and the CPU isn't near that. It's all rather inelegant.

In my opinion, the power supply should be set up the other way around—the vents in the casing should draw hot air in from the case, and the fan should blow it out of the power supply. In the photo, it’s the other way around, unless you also have vents on the bottom.

Ydee wrote on Yesterday, 09:14:

In my opinion, the power supply should be set up the other way around—the vents in the casing should draw hot air in from the case, and the fan should blow it out of the power supply. In the photo, it’s the other way around, unless you also have vents on the bottom.

You are saying the same thing as me.

However, an ATX PSU can't go the other way up without cutting the rear of the AT case to make space for the socket and fan swapping sides - note the PSU opening in the AT case has a rounded side for fan, and square side for power sockets! Now imagine flipping the PSU over - doesn't fit, right?

In 1995, Intel wrote Advanced Technology eXtended v1.0 upon which everything should change, but most of the changes are just different for the sake of being different. We are now on ATX v3.x, and there is still no centralised archive or library with historical specs.

I doubt many people have been tracking the changes - or realised Intel keeps setting new ticking time bombs to contain PC life expectancy.

Some older ATX power supplies don't have air intake vents on the bottom, but rather on the side opposite the fan and the power cable socket. These might be compatible with your case. Like this one:
https://computercyber.com/products/new-origin … b-atx-ps-7270c/

Ydee wrote on Yesterday, 13:01:

Some older ATX power supplies don't have air intake vents on the bottom, but rather on the side opposite the fan and the power cable socket. These might be compatible with your case. Like this one:
https://computercyber.com/products/new-origin … b-atx-ps-7270c/

That would mount correctly and it's a good suggestion for the problem as I described it, but I don't think it suits my world.

The EVOC PS-7270F actually an industrial server PSU.

Part of the reason I can embrace swapping AT original for an ATX PSU on my AT/ATX transition i430TX is that I see value in audio capabilities. The i430TX isn't strong for audio production, but it's solid for playback - I might install my Dxr2 kit and a sound card that natively supports 44KHz CD + 48KHz DVD sources. That is where an industrial server PSU might clash.

Home AT machines had a passthrough power cable so one whole complete PC system was conveniently powered from exactly one plug - even AT era active speakers had passthrough splitter cables. The EVOC breaks that feel. Home ATX machines break that feel too, but introduce a different home feel - more heat, bigger fans, quieter cooling.

I'll give it some thought..

Of course, that link was just for illustration—to show a type of PSU with holes on the sides rather than on the bottom. Depending on your needs, you can also find other high-quality PSUs that use this type of cooling system.

MattRocks wrote on 2026-04-11, 11:57:

And given the PSUs have changed, and many flavours are no longer made, should old PSUs now be given more TLC? Should I even be repairing my AT PSU?

If you have the time and the skills (or are willing to learn), why not?
Otherwise, you can just chuck them back on the bay or whatever other site you prefer and hope someone else who's into PSU/old PC restoration to find them and buy them.

I personally prefer to restore PSUs almost all of the time - even the not-so-great ones. Only the really crappy gutless wonders with poor designs and PCB layout I leave for parts. Just about everything else gets fixed (but slowly 🤣).

And by the way, that PSU on the picture in your 2nd post looks like an FSP (Fortron/Source/FSP Group) and a rather old unit at that, judging by the heatsinks seen through the vents and the stickers on top ("W/ Noise Killer"). No surprise if it exploded or didn't work after all this time. These older FPSs often used Fuhjyyu -branded capacitors inside that always failed. The 5VSB in particular is known to commit suicide when its output caps go bad. A lot like the FSP in this thread:
(SOLVED) FSP300-60GTF repair - blown transoptor, resistors, worth it?

That said, the nice thing about some of these older ATX PSUs is that they often use widely available parts that are still manufactured today, which makes sourcing the parts for the repair a lot easier to find.