You can buy new AT PSUs on Amazon. There are currently Athena Power AP-AT30 and AP-AT40 models for 300w and 400w respectively. I've been using the 400w model off and on with a Pentium 233 MMX test bench setup for the past couple of years without any problems.

mscdex wrote on 2023-03-07, 18:19:

You can buy new AT PSUs on Amazon. There are currently Athena Power AP-AT30 and AP-AT40 models for 300w and 400w respectively. I've been using the 400w model off and on with a Pentium 233 MMX test bench setup for the past couple of years without any problems.

Nothing showing up on Amazon 🙁 I'm guessing you're not in the UK?

Ah, that could be it then. I am using the Amazon U.S. site.

You'll probably be better off with one of those ATX->AT adapters then. Those at least seem to be available on U.K. eBay.

There is a "AT power supply unit FSP300-60PNA(PF)(AT)" for £45.00 on eBay UK.
It has remark: This is not an original AT PSU.

This a modified ATX PSU suitable for AT systems. This PSU is 25mm longer than standard original AT PSU. please check there is enough room in your machine.

I've got a couple of relatively new ATX power supplies in my spares box, can I just purchase one of the ATX to AT adapters or will they only work with a specific type of ATC power supply. I've not really paid attention to PSU technologies over the years, i just make sure I buy the right power supply at the time of purchasing a new motherboard etc.

Are all ATX power supplies suitable to use with an ATX to AT adapter to power up old AT computers or are there ones to avoid?

FazzaGBR wrote on 2023-03-08, 09:54:

Are all ATX power supplies suitable to use with an ATX to AT adapter to power up old AT computers or are there ones to avoid?

Pretty much Anything will do!

That means:

• Enough current on each line - in practice this is trivial even for a modern "weak" 350 W affair (I just said to ignore total wattage, heh), if you don't push your choice of "AT" with 2000s stuff
• No -5 V - but unless you have a PC (=IBM 5150, and even then only the motherboard with maximum 64K integrated) you almost certainly don't need one for the base system, and you can see on this very forum countless circuits to create it (available in the form of an ISA card or directly on the motherboard cable)
• Whether you really have an AT connector - sometimes it's blatantly not (Olivetti PCS 286), sometimes it's a lookalike, but should be easy to check if you have any ISA slots because the pins are nicely accessible for a continuity tester 😀

Of course some products on the market are going to be crap, but that's always been true (and it seems to be generally agreed that the median cheap power brick is better now than then)!

Indeed, the only PSU I've ever bought separately (last year) is an used PowerMan FTX thing for 10 €!

It's purely for this Socket 5 Pentium 100 PC I've just purchased so by the sounds of it an ATX to AT adapter will be perfect! Just ordered on on eBay so it should be with me in a few days time. The existing PSU works fine but I'd rather not take the risk of using a 28 year old PSU all the time so replacing it with a new one is what I'm going to do.

Thanks everyone!