Yes. You might need to place it upside down for the back screws to fit in properly. I'm using a 500W ATX PSU in a Mid-Tower AT case. (500W - Just used the extra PSU I had in hand.)

Definitely use an ATX psu if you can - you don't have live current flowing through the on/off switch and, as you say, they tend to be a lot higher quality than the old AT designs.

megatron-uk wrote:

Definitely use an ATX psu if you can - you don't have live current flowing through the on/off switch ...

I often wondered about this. Are you familiar with AT to ATX PSU adapters? I wondered if there was live current flowing through its on/off switch. Actually, thinking about this a bit more, I doubt it. I hope not anyway, because I just press the "bare" power button (which itself is not earthed / attached to the case) with my finger.

There's no live current on the ATX power switch.

On AT power supplies it was live current, and the better solution IMO, as there was no standby current and you could switch off the monitor and other small devices too. But the energy wasters won...

h-a-l-9000 wrote:

There's no live current on the ATX power switch.

Do you mean - there is no live current on the "AT style" power switch which is part of the AT to ATX PSU adapter ?

There is no live current on any part of a usual ATX PC except inside the power supply.

Thanks a lot for the info!

The 'switch' on an ATX psu, and as shown on the ATX/AT cable above is simply a momentary push button - it doesn't stay live once pressed.

On the ATX to AT cable it must be a 'permanent' switch for it to work. An ATX mainboard does the momentary - permanent conversion. AT mainboards don't have that feature so the switch has to provide that itself.

(Wonder how often that has to be repeated...)

Yes, when you press the power switch on an ATX to AT PSU adapter cable, it stays down and when this happens, power is sent to the AT mainboard. If you press the adapter's power switch again, this switch goes up, and power is not sent to the mainboard anymore.

h-a-l-9000 wrote:

There is no live current on any part of a usual ATX PC except inside the power supply.

There has to be, otherwise shorting the front panel "power on" wires wouldn't do anything, right??

About the ATX in AT case subject, if you have an ATX PSU in mind for using in an AT case, be wary that many AT cases have a horizontal "plate" where the AT PSU is placed on.
AT PSU's usually have their air openings in the back, right next to the optical drives.

ATX PSU's often have either a fan on the underside of the PSU or the air openings are on the bottom of the PSU, which will be blocked by that horizontal plate of the AT case!

I meant there is no current there that is *not* decoupled from the 'live current' of the power outlet (would be dangerous to touch). Of course there is the 5V standby voltage, which might not even kill ants.

AT power supplies have the thick black cable to the power switch. This is real live current and if the connections to the switch are not isolated you need to be very careful (or better: don't even plug it in).

Tetrium wrote:

h-a-l-9000 wrote:

There is no live current on any part of a usual ATX PC except inside the power supply.

There has to be, otherwise shorting the front panel "power on" wires wouldn't do anything, right??

I think they all left out the key word "mains". 😉

Obviously no live mains outside an ATX PSU. Only PWR_ON and 5VSB are live until the system is powered up.

Yes, mains seems to be the correct word 😀

h-a-l-9000 wrote:

I meant there is no current there that is *not* decoupled from the 'live current' of the power outlet (would be dangerous to touch). Of course there is the 5V standby voltage, which might not even kill ants.

AT power supplies have the thick black cable to the power switch. This is real live current and if the connections to the switch are not isolated you need to be very careful (or better: don't even plug it in).

Thanks for clearing this up! 😁

Indeed, 240v (and 120v in the US) is very much different from the weak 5v.

Iirc I once fried a board when I plugged in the powercord (had jumper set to clear CMOS) even though the power switch was turned off...I think?
The 5vsb is probably also powering the flash ROM and the BIOS battery takes over when the system is completely disconnected, right?
Dang 🤣, 13:37pm but I feel like it's 7am in my head! 😜

Edit:But anyway, the vast majority of the ATX PSU's I come across for which I think "Hey, this would make an excellent PSU for an AT board!" has the vent holes in the bottom of the PSU. For me an excellent ATX PSU for an AT case is like a 235W high quality (but second hand) ATX PSU as 235W is kinda sucky for almost any ATX rig, but I find I'll probably have to saw in extra vent holes for it so air can actually more through the PSU (and also remove hot air from the insides of the AT case).

AT cases look really cute!! But their design was getting very limited towards the end of it's reign....but they look so nice! 😁

Every time I work inside an AT case I'm like "My god...cmon stuped cable, stay there!...ouch, another cut in my finger!" but when I'm finally done and have the closed system case powered on and such...THE JOY! L O L!

The ATX spec for the Power Switch is an active GROUND signal.

It's pulled high until the switch contact is made and then it goes to a ground signal or zero basically.

Wiki has a interesting ATX article too:

http://en.wikipedia.org/wiki/ATX#Power_switch

Robin4 wrote:

First AT PSUs really sucks big time!! Few minutes ago my AT PSU is stopt working.. Maybe the fuse is broken (i dont know) But th […]
Show full quote

First AT PSUs really sucks big time!!
Few minutes ago my AT PSU is stopt working.. Maybe the fuse is broken (i dont know) But the quality of those AT PSU lacks very much. Now i need to have an new PSU.. I looked already on ebay, but most of the sellers only sending to own country in america..

I don`t think the high prices with high shipping cost itsnt an good idea to buy an other AT PSU again. Also because the quality sucks big time..

I was thinking to use an older ATX psu (without SATA power)
Would this unit fit in an AT case?

The only company still making AT power supplies isn't exactly known for building top quality parts. Most of the older AT power supplies that you find either used or NOS are probably suspect as well just due to their age and certain internal parts (*cough* caps *cough*) not holding up well over time. A wiring harness adapter is the best thing to adapt a standard ATX PSU but be sure you find a PSU with the old style connectors on it. You shouldn't need anything other than the standard ATX motherboard connector(s), a handful of Molex connectors, a floppy connector and maybe a small 4 pin for attaching to a video card. You don't need SATA, PCIe/AGP Pro, or SLi or Crossfire compatibility with a vintage machine. You shouldn't need an insane amount of wattage, either. I probably wouldn't use more than 550W with any machine from a PIII backwards but I'm sure someone has a machine that requires more than that, I just can't think how they would need that much on a machine so old unless they were running a dual Xeon server with 10 hard drives and an AGP Pro video card. (Or an ALR Quad 6 or 6x6)

A generic 235W ATX PSU should be enough for any P1 or lower spec-ed AT rig. Mind you, an El Cheapo PSU is not a generic PSU, it's a heap of junk 😜

sliderider wrote:

... You shouldn't need an insane amount of wattage, either. I probably wouldn't use more than 550W with any machine from a PIII backwards but I'm sure someone has a machine that requires more than that, I just can't think how they would need that much on a machine so old unless they were running a dual Xeon server with 10 hard drives and an AGP Pro video card. (Or an ALR Quad 6 or 6x6)

... and even then if you do have something along those lines, such as a server, you have to ask yourself; "is it worth running such a 'seemingly' beast of a machine?".

A short time after buying my house I replaced two dual processor machines; a dual P3-933 on an ASUS CUR-DLS and a dual AMD Athlon 2800MP on a Gigabyte DPXDW. One was my filestorage/av store of 3.5 Tb, and the other my website/email/development system.

All of those services are now on an AMD X4 6400 HE processor (45w) and the disk service has been reduced from 8 x 500GB SATA disks, to 5 x 1Tb. It's a lot quieter, a lot cooler, uses only 1bar of power on my UPS, compared to 2+ *each* for the dual systems, and actually, is massively quicker too.

I get the appeal of retro kit (check out my videogame database sometime), but sometimes it makes more sense to use modern equipment for 'work' purposes (by 'work' I mean that in the broadest sense - ie providing a service).