On an old machine, the PSU died, and I attempted to change it. However, the power connector to the motherboard seems to be a weird 12 pin connector, and I can't seem to find any adapter with the typical 20/24 ones.

What can I do with these? I am not even sure those really are what I think they are.

The computer actually isn't mine; I am just trying to help out a friend. He has a proprietary software installed on it to maneuver a professional cutting machine, and it can't be installed on another machine. I thought about putting the hard drive in another computer and trying to boot from it, but I am afraid the difference in hardware would make the Windows 98 unable to work. I fear to make "permanent" damage on the system that would require tedious fixing afterwards.

Here is the motherboard connector slot :

enter image description here

The old PSU's connectors (a bit blurry sorry) :

enter image description here

The old PSU model :

enter image description here

And the "new" PSU's connector with 20 pins :

enter image description here

  • Max output power 74W? wow. – user253751 Sep 11 '17 at 23:52
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    @Braiam No, it looks like that is about what you get from adding up the V*A of each rail, however some of those are obscured by a reflection. – user253751 Sep 12 '17 at 1:18
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    This question is better suited for retrocomputing.stackexchange.com – Agent_L Sep 12 '17 at 15:32
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    This isn't some unknown weird power supply, it is Compaq presario power supply (a weird but known power supply) the part number is listed right there in the photo 337373-001. See my answer for some places to purchase replacements. – Justin Ohms Sep 12 '17 at 17:51
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    @Hastur I get your point, but my point was more that it wasn't really unknown, it literally has the part number on it. – Justin Ohms Sep 13 '17 at 18:33

EDIT: I appreciate all the thumbs ups, but as other users have pointed out this is likely not an AT connector. After doing more research, my best suggestion to the OP is to purchase the original part number item to insure compatibility with this system. There are no second chances, once the wrong power supply is plugged in, the motherboard is toast.

It appears, based on research, that this system is a Compaq Presario 22xx series. The specs of that series, and references to the original power supply part number suggest that this is an ATX style power supply. The extra 6-pin plug is typically an auxiliary connection. However, it is highly likely, as suggested by other commentators that this is a completely proprietary power supply. A lot of manufacturers are guilty of creating non-standard systems around this era. I cannot find any standard power supplies that used 12 pin AT/PC style power connectors and a 6-pin auxiliary connector. What is for sure, is that this power supply (not clearly seen in the OP's photo) is also proprietary in shape and size:

enter image description here

So, I have left the original message below, but I think it is prudent to not take chances given the sensitive nature of this repair. Just spend the money on getting the exact original part number.

----- ORIGINAL ----- The connector on your motherboard is an AT connector. The power supply you are trying to hook up is an ATX connector.

You'll need to buy an AT power supply. When you hook it up make sure you attach the two motherboard power connectors with the black wires next to each other.

enter image description here


Now, I have to ask - What are you doing with this computer from 20+ years ago?

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    @AngryCub Your friend obviously relies on this computer to remain operational. It might be time to upgrade whatever components rely on this ancient technology. You might fix this problem. You might not be able to fix the next one. – I say Reinstate Monica Sep 11 '17 at 19:18
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    @Twisty it's an all too common problem, someone builds a peice of industrial equipment around a PC and then the PC dies long before the industrial equipment does. Often your only options are to try and fix the retro PC, pay someone to do a custom control system or replace the machine entirely. – plugwash Sep 11 '17 at 19:52
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    @plugwash I know. I've been there. It's better to face that reality while things are working than wait until a production machine is down and orders aren't getting filled. – I say Reinstate Monica Sep 11 '17 at 19:54
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    If the software only works on Windows 98 you still might be able to get it running on a modern computer in a VM. – user253751 Sep 11 '17 at 23:53
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    Check out retrocomputing.stackexchange.com. With plenty and cheap replacement parts, running a 286 is both easy and economical in 2017. Adapting an old system to accept a new computer can turn out much costlier than buying few ancient PCs off ebay to cannibalize. OP's PC ran for at least 20 years, give it some credit! – Agent_L Sep 12 '17 at 15:36

This is a Compaq Presario desktop power supply. (That is what the Compaq spares number indicates.) Compaq was notorious for inventing their own slightly non-standard wiring configurations for power supplies and motherboards. It is neither an AT or an ATX power supply.

You can find reconditioned units but they are expensive here are a few I found.

Memory 4 Less
Impact Computers

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    If you could provide pinout for this "weird but known", it would be pretty straightforward to construct an adapter for far less than $200. – Agent_L Sep 12 '17 at 20:48
  • @Agent_L Personally I wouldn't recommend that, better to replace with the correct part. I'm sure if someone wanted to do it they could find pinouts somewhere. – Justin Ohms Sep 13 '17 at 18:44

As mentioned in the other answer that is an old AT style power connector.

It is possible to connect an ATX power supply using an adapter but there are a couple of caveats.

  1. Your system may need -5V which modern ATX PSUs don't have (some but not all older ones do)
  2. AT power supplies are not controlled by the motherboard but by a seperate power switch. The adapter is likely to have a pair of wires for connecting to your power switch. Depending on your case design you may be able to hook up the existing power switch or you may need to fit a new one to the case somehow.
  • No, it's not. There is no -5V in this PSU, but there are ATX lines (+3.3V, +5VSB). Also, there is a third P-plug. This is not your regular AT, it's some kind of hybrid. – Agent_L Sep 12 '17 at 16:01

This is neither ATX nor AT power supply. The 2 main plugs (P8 and P9) are regular AT, but there is also an unaccounted for third one and PSU provides +3.3V and +5VSB rails which is something that AT PSUs don't do. Also, it doesn't have -5V rail, which regular AT should have.

My guess is that's an intermediate-era PSU, which internally is ATX (hence the ATX-like configuration of lines), but uses 2 AT-style connectors + a proprietary 3rd one. Your best bet IMHO is to seek help from some hacker with basic soldering skills. Cables from the dead one could most likely be combined with a working ATX PSU to get an operational replacement.

There is a possibility that the 3rd connector is P10/P11 which supplies 3.3V, but if that's the case, where does +5VSB line go? You can buy an ATX to AT-with-P10 adapter, but if the 3rd one is not P10 but proprietary (with +5VSB), it can end badly.

Try asking at https://retrocomputing.stackexchange.com, maybe someone will recognize the setup. But provide better pictures of the plugs and motherboard, with visible cable color configuration and markings.


A quick google search will soon give many results for AT power supplies Adaptors for ATX seem quite mad, particularly given that:

The machine is for a control machine, so Im assuming that there is an (ISA?) card interfacing the hardware. There may be a custom BIOS for the control card making moving it very difficult.

Add in cards may need -5 V even if the motherboard doesn't need it to boot, so if you try converting an ATX PSU be prepared for the machine to not control anything, even if it powers. Like the other answers say, get an AT power supply.

I'd also image the hard drive whilst I was about it so this can be replaced if it goes.

EDIT After seeing the other answer, that this is neither AT or ATX, a google search of the part number on the PSU indicates this came from a Compaq Presario. Those things use ATPWR psu, so you'll need a compaq power supply - completely non standard.

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