The AT power button has four cables that are connected directly to the mains power outlet, so you should be very careful and not touch those when it's connected. The ATX psu is different. Power goes in, and there only a switch to activate it. I guess if you want to use an AT case power switch it's easy. Instead of connecting 4 cables, you only need to connect 2. I think the ATX to AT converter switch may also be designed for 4 cables(at least the one I have), but it has only two connected.

>Additionally, I'm curious as to how much of a deviation is acceptable

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

"Generally, supply voltages must be within ±5% of their nominal values at all times. The little-used negative supply voltages, however, have a ±10% tolerance. There is a specification for ripple in a 10 Hz–20 MHz bandwidth:"

Generally these power supplies need loads on both 5V and 12V to put out the correct value.

The -5v line is only a problem for a few selected older cards on the isa bus. There's a thread here listing some of the cards that need it here: The Mystery -5V Rail

Its soooo easy to make -5V from -12V...

Which converter do you use Markk?

Don't ATX power supplies use momentary switches? Short briefly to turn on, and again to turn off? If you use an AT switch wouldn't that just either close the circuit or open it? If you keep the leads shorted on any of my ATX power supplies it'll turn on the computer, and then just turn it off (and it'll stay off).

@h-a-l-9000: Thanks for the info on tolerances. I guess they are the same for AT systems.

@megatron-uk: Thanks; looks like I will be needing the -5v lead. I'm going to be running a LAPC-I and Sound Blaster Pro...

ACSKJP wrote:

Don't ATX power supplies use momentary switches? Short briefly to turn on, and again to turn off? If you use an AT switch wouldn't that just either close the circuit or open it? If you keep the leads shorted on any of my ATX power supplies it'll turn on the computer, and then just turn it off (and it'll stay off).

That's correct. Instead of using the motherboard's power switch header, you can instead cut the green PS_ON wire and a black earth wire on your PSU's motherboard connector, and put the AT power switch between them.

If you wanted to use an ATX PSU and board in an AT case you can do this too. You will probably need to put a jumper over the ATX power on header, and set the BIOS to not shut down if the power button is depressed. (By default I believe most boards will shut down if the power button is depressed for 4 seconds).

ACSKJP wrote:

@megatron-uk: Thanks; looks like I will be needing the -5v lead. I'm going to be running a LAPC-I and Sound Blaster Pro...

A Sound Blaster Pro doesn't need it AFAIK. Only Sound Blaster 2.0 (CT1350)
See here for info on different Sound Blaster and SB PRO models.
http://en.wikipedia.org/wiki/Sound_Blaster#Fi … A_.26_MCA_cards

ACSKJP wrote:

Which converter do you use Markk?

Don't ATX power supplies use momentary switches? Short briefly to turn on, and again to turn off? If you use an AT switch wouldn't that just either close the circuit or open it? If you keep the leads shorted on any of my ATX power supplies it'll turn on the computer, and then just turn it off (and it'll stay off).

Well that's correct, but you are talking about the ATX power switch which is connected to the motherboard, which sends a signal to the PSU to power on. But if you want to force an ATX PSU to power on, you just need to connect the green cable on the ATX connector with a ground(black). So that's what the ATX to AT converter does. And you need a permanent switch, otherwise it's going to turn off the moment you disconnect those cables. Here's a pic of the one I have :

Wow, thanks a lot everyone. I'm starting to remember this stuff. I think I used to stick a paperclip in ATX power supplies to start them up without anything else - so that would be doing the same thing as an AT switch. I guess I'll have to either find a stable AT power supply, or an ATX power supply with the -5v leads. Thanks!