Many AT - PSU (e.g. for the original IBM AT) have the power switch on the side of the case and directly build into the PSU unit. They are also often designed for a specific case (in some particularly poor design solutions a front switch is connected to the PSU switch with a long metal rod). fitting a new ATX PSU into an older AT case should be not too complicated. But what is your solution for the power switch on these machines (without remodelling the case / 3D printing new switches etc.).

As the poster above mentioned, it's worth distinguishing "big orange switch" true AT power supplies from "pushbutton on a leash ones" which seem to be closer associated with LPX or "PS/2" (though my PS/2s used the Rube Golberg trick of a metal rod from the front power switch to a second one on the PSU).

I have also seen this topic bounced back and forth, with some suggesting that the nadir in quality was the first $700 PC era (very late 90s and early 2000s) and those from earlier than that might be worth saving?

It really depends on the brand and model.

However, I use ATX with an adapter and added -5v if needed in place of AT power supplies when possible.

I'm also generally pretty picky about what ATX PSUs I use.

Keep in mind whole 5V vs 12V thing.

Yes, PCs in question should not draw enough power to overload modern PSUs 5v rail, but there is one issue here - on typical PSU with group regulation atypical load, even not close to maximum limits, can cause issues. Like draw 50W on 5V rail and near zero on 12V an voltages will drift - 5V will go down, 12V - up.

So you'd probably want one based on DC-DC design (12V PSU + DC-DC converters for other voltages, better modern PSUs tend to be built like this) for this purpose.

Other than that yeah, i like using modern power supplies, if nothing else because of reduced noise....

Also there is an annoying combination of ATX power supplies always being short on "floppy" power connectors (sometimes none), and every little internal dongle device finding it perfect to use one (like IDE-CF and StarTech) IDE-SATA

Aui wrote on 2025-05-26, 02:50:

Many AT - PSU (e.g. for the original IBM AT) have the power switch on the side of the case and directly build into the PSU unit. They are also often designed for a specific case (in some particularly poor design solutions a front switch is connected to the PSU switch with a long metal rod). fitting a new ATX PSU into an older AT case should be not too complicated. But what is your solution for the power switch on these machines (without remodelling the case / 3D printing new switches etc.).

I am certainly talking about the generic PC AT PSUs here, none of the special or custom PSUs.

The ones with the side switches and similar, crappy or not, will need to get recapped/reworked. I'm not as worried about those because there is at least some obvious value in saving them. A generic AT PSU though? I don't see it.

Archer57 wrote on 2025-05-26, 03:02:

Keep in mind whole 5V vs 12V thing. […]
Show full quote

Keep in mind whole 5V vs 12V thing.

[snip]

So you'd probably want one based on DC-DC design (12V PSU + DC-DC converters for other voltages, better modern PSUs tend to be built like this) for this purpose.

Other than that yeah, i like using modern power supplies, if nothing else because of reduced noise....

Right! I do pay careful attention to the +5V rail ratings on the PSUs I am considering. I like to make sure they are rated to supply a minimum of 20A on that rail.

You do make a good point about the DC-DC design and I will be on the lookout for those especially.

jakethompson1 wrote on 2025-05-26, 03:02:

Also there is an annoying combination of ATX power supplies always being short on "floppy" power connectors (sometimes none), and every little internal dongle device finding it perfect to use one (like IDE-CF and StarTech) IDE-SATA

UGH. Yeah. I have a stock of molex to floppy adapters just because of that.

What are you basing your judgment on to determine whether an AT power supply is bad or not? Most standard units used on generic Baby AT cases or desktops share the same tried & tested basic design, with the main difference being the quality/rating of the components used. An old Delta or Astec AT PSU may look totally generic, but is usually of very good quality and will last a long time, especially after a simple refurbish (new capacitors + fan).

As for me, I ALWAYS go with (decent) old AT power supplies on AT style systems for the following reasons:

• Much cheaper to buy a few caps + 80mm vs. a new modern PSU and all required adapters
• ATX-AT adapter + SATA-Molex + SATA-floppy adapters make those cramped Baby AT cases even messier
• Modern PSUs normally have the fan on the bottom side, but it ends up facing up or just blocked altogether in many old cases
• Most importantly, a new black power supply looks completely off in an old case, so you lose a lot of retro style points there 😛

If I were to go with a modern solution, I'd probably replace the guts of an AT PSU case with something newer to keep the adapters hidden inside while also maintaining an original "look". But in the end it's just cheaper to get and refurbish an old AT PSU as nobody seems to want them anymore. Delta, Astec, HIPRO, Enermax, Seasonic and more are usually built like tanks and very reliable, it's just that PSU branding wasn't a thing back then as it is now.

People keep peddling the idea that AT units are "dangerous" but I've yet to see actual evidence for that other than circumstantial experiences, most pre-2000 PC hardware is incredibly resilient and keeps chugging on for decades with "dangerous" power supplies unless it's killed by corrosion or physical damage. Bottom line, I just don't see any significant advantage in cost, performance or safety on using modern units on AT style boards.

TheMobRules wrote on 2025-05-26, 04:19:

What are you basing your judgment on to determine whether an AT power supply is bad or not? Most standard units used on generic […]
Show full quote

What are you basing your judgment on to determine whether an AT power supply is bad or not? Most standard units used on generic Baby AT cases or desktops share the same tried & tested basic design, with the main difference being the quality/rating of the components used. An old Delta or Astec AT PSU may look totally generic, but is usually of very good quality and will last a long time, especially after a simple refurbish (new capacitors + fan).

As for me, I ALWAYS go with (decent) old AT power supplies on AT style systems for the following reasons:

• Much cheaper to buy a few caps + 80mm vs. a new modern PSU and all required adapters
• ATX-AT adapter + SATA-Molex + SATA-floppy adapters make those cramped Baby AT cases even messier
• Modern PSUs normally have the fan on the bottom side, but it ends up facing up or just blocked altogether in many old cases
• Most importantly, a new black power supply looks completely off in an old case, so you lose a lot of retro style points there 😛

If I were to go with a modern solution, I'd probably replace the guts of an AT PSU case with something newer to keep the adapters hidden inside while also maintaining an original "look". But in the end it's just cheaper to get and refurbish an old AT PSU as nobody seems to want them anymore. Delta, Astec, HIPRO, Enermax, Seasonic and more are usually built like tanks and very reliable, it's just that PSU branding wasn't a thing back then as it is now.

People keep peddling the idea that AT units are "dangerous" but I've yet to see actual evidence for that other than circumstantial experiences, most pre-2000 PC hardware is incredibly resilient and keeps chugging on for decades with "dangerous" power supplies unless it's killed by corrosion or physical damage. Bottom line, I just don't see any significant advantage in cost, performance or safety on using modern units on AT style boards.

Well said

TheMobRules wrote on 2025-05-26, 04:19:

What are you basing your judgment on to determine whether an AT power supply is bad or not? Most standard units used on generic Baby AT cases or desktops share the same tried & tested basic design, with the main difference being the quality/rating of the components used. An old Delta or Astec AT PSU may look totally generic, but is usually of very good quality and will last a long time, especially after a simple refurbish (new capacitors + fan).

I'm not saying this because it looks generic. If it was from any of the brands you listed in your post then I wouldn't have said what I did. I am familiar with those companies and know they make quality PSUs. In this particular instance, looking inside the PSU everything about it says "minimum cost." The caps are garbage tier (Fuhjyyu) and other unidentifiable generic Chinese components. The only component in the entire PSU that is from a recognizable company is a single ST microcontroller IC.

I'm all for saving quality AT PSUs, but this isn't one of them.

Can we see some pictures of the PSU? (With the covers removed, obviously. 😉 )
I've refurbed/upgraded a lot of "not worthwhile" PSUs into decent ones and still continue to do that from time to time. It's hardly any extra work on top of a recap job. The not-too-terrible cheapies usually either lack the primary side EMI/RFI filtering components (common-mode chokes, X2 and Y2 caps, and etc.) or skimp on some of the output filtering components (e.g. smaller and/or less capacitors and free spots for them.) The former I remedy with the help of scrap PSU boards from scrap LCD TVs (lots of them nowadays). The latter I remedy when I do the recap - I simply put the right/properly-sized parts that the PSU should have (e.g. 2x 2200 uF caps on the 5V rail as minimum.)

TheMobRules wrote on 2025-05-26, 04:19:

What are you basing your judgment on to determine whether an AT power supply is bad or not? Most standard units used on generic […]
Show full quote

What are you basing your judgment on to determine whether an AT power supply is bad or not? Most standard units used on generic Baby AT cases or desktops share the same tried & tested basic design, with the main difference being the quality/rating of the components used. An old Delta or Astec AT PSU may look totally generic, but is usually of very good quality and will last a long time, especially after a simple refurbish (new capacitors + fan).

As for me, I ALWAYS go with (decent) old AT power supplies on AT style systems for the following reasons:

• Much cheaper to buy a few caps + 80mm vs. a new modern PSU and all required adapters
• ATX-AT adapter + SATA-Molex + SATA-floppy adapters make those cramped Baby AT cases even messier
• Modern PSUs normally have the fan on the bottom side, but it ends up facing up or just blocked altogether in many old cases
• Most importantly, a new black power supply looks completely off in an old case, so you lose a lot of retro style points there 😛

If I were to go with a modern solution, I'd probably replace the guts of an AT PSU case with something newer to keep the adapters hidden inside while also maintaining an original "look". But in the end it's just cheaper to get and refurbish an old AT PSU as nobody seems to want them anymore. Delta, Astec, HIPRO, Enermax, Seasonic and more are usually built like tanks and very reliable, it's just that PSU branding wasn't a thing back then as it is now.

People keep peddling the idea that AT units are "dangerous" but I've yet to see actual evidence for that other than circumstantial experiences, most pre-2000 PC hardware is incredibly resilient and keeps chugging on for decades with "dangerous" power supplies unless it's killed by corrosion or physical damage. Bottom line, I just don't see any significant advantage in cost, performance or safety on using modern units on AT style boards.

Amen. 😀

LChackr wrote on 2025-05-26, 03:03:

Right! I do pay careful attention to the +5V rail ratings on the PSUs I am considering. I like to make sure they are rated to supply a minimum of 20A on that rail.

The problem is not so much the size of the 5v current rating, but how the PSU will react when you load the 5V rail more than the 12V rail.
Modern group-regulated PSUs tend to cross-load poorly if a bigger portion of the load is on the 5V rail than on the 12V rail regardless of how much current the 5V rail is rated for. Not that this would stop an old PC from running or break it... usually.