Your case has a power supply with the same form factor as the IBM PC AT 5170, i.e. a "true" AT power supply.

You can definitely use an ATX power supply with that motherboard, but there are a few things you need to resolve to make it work:

1. Replace the current power switch with a momentary one that you can connect to the motherboard header
2. Adapt the ATX power supply or the case to fit properly
3. Given the distance between the PSU and the motherboard, you will probably need extra long power cables or extensions

For adapting the PSU to the case, one way would be to cut the back of the case, but it would be a shame to do that. You can also transplant the guts of the ATX power supply into the enclosure of the old one, but that will probably require soldering and/or creative thinking to make it fit properly.

Personally I would just open the existing PSU and do a basic refurbish (replace fan and capacitors), unless it's of really bad quality.

Yup, I saw the kind of ATX-to-AT adapter that Phil's Computer Lab used on YouTube with the -5V and the power switch. I'd need something like that but without the AT plugs I guess.

The cable length might not be an issue to be honest based on the internal layout. The ATX plug on the motherboard is right at the top and the drives wouldn't be an issue either in terms of cable length.

The issue would be how to mount the PSU in the case but there two metal bars under the PSU, one to each side of the PSU and maybe I could zip tie or something like that an ATX PSU to those (random thought that just came to mind). But I don't think it would be impossible. Just not as good looking as the original PSU is as it fits the case.

I'm not in a hurry to jump the gun to get a PSU as currently the PC works, I just need to sort out the soundcard situation (see my previous post) and I am looking to add some ventilation to the case. I've already mounted a 120mm molex powered fan at the front bottom, the Voodoo has a 60mm molex powered fan zip tied to it and I will try to add one of those PCI slot fans below the PSU to add some additional exhaust besides what the PSU offers.

If anyone has a link to the kind of adapter I would need to add that -5V (don't even know if it's mandatory for this PC) and the power button when using an ATX PSU, please share.

Something interesting, someone has modded the case so that the display on the front shows 40 or 20 depending on pressing the Turbo button, but the turbo connector is obviously not connected to the motherboard.

Anyway, the PC works, I haven't games for more than 5 minutes on it to see if there's issues yet.

I am enquiring about a modern PSU as I don't know how reliable the current PSU is and I don't have the knowledge or skill to recap it.

There's no modern replacements sold that I'm aware of, having looked for one a couple times in the past to replace a failed one.

The power supply is technically referred to as "IBM AT tower" format. The format was identical to the IBM 5170 power supply, except using the standard four wire connected front power switch versus the side mounted rocker.

A few notable companies like Enermax made supplies in this form factor. They are relatively reliable as supplies go, albeit inefficient. There's a lot of guides on recapping and repairing them out there, I have not heard of a modern ATX replacement for one. You can probably get a bracket made to mount a regular ATX power supply in the case without it looking bad cosmetically.