That's crazy. Sorry to hear about it. Sucks. As to your question, no idea. I've had systems turn themselves on, but it was some kind of device like a wireless adapter meshing with some kind of BIOS setting allowing that.

Seems a bit much to toss out all old power supplies, but since I don't know what happened here, I can't help.

I'm 34 too. How'd we get so old? 🤣

The lesson to learn: Never leave old hardware connected to mains when you are not using them.

^*Ahem* this reminds me of our "old" LED bulbs at home. The ones that run 24/7 do work for years, whereas the ones that we do switch on/off on a regular basis won't last 6 months even. 😉

Can't hurt to open up the other PSU's and check.

I've stopped using old ATX PSU's since getting back into retro PC's. All new builds use the same brand modular power supplies, that way I can use the spare molex cables from my sata based pc's in my ide based systems and not have a bunch of "useless" sata power connectors as the cables are standardized.

My 2 AT rigs on the otherhand I need to do something about, but haven't.

Maybe it would also be a good idea to shut the power off at the power bar after you've done a soft power off.
I've never liked soft power off, precisely for the reason you've discovered. Just recently I almost had a laptop bake itself to death after I shut it down and closed the lid. It woke up again while closed and in my computer bag. Thankfully I was around and smelled the burning plastic. Somehow it still works, but maybe something would have caught fire if I had stepped out.

That charred area is responsible for +5V standby voltage regulation, purple wire coming from there confirms it. Perhaps an electrolyte, that leaked from el. caps, reached the primary, high voltage side of a SB transformer. Any voltage, higher than 5V, would easily damage semiconductor logic on a motherboard, that is responsible for a soft power-on. I can see that one of the caps in that PSU is of a "CapXon" brand, which is infamous for being called "CrapXon" for its poor quality.

There is nothing wrong in using period correct PSUs in old PCs, as long as you can identify possible hazards that may cause it to fail in the future. A well designed old PSU is just as reliable as any modern, good brand PSU. Personally, all of my old systems are using period correct PSUs. You may want to recap those "Allied" PSUs with known good brand el. caps, because it's just a matter of time when they'll fail in a similar fashion.

I would use a new power supply on something as modern as a high end Pentium 3 if you aren't able to at least recap the psu in advance of use. Chances are you wont be using any devices that requires -5v. I also find that PSUs from the early 2000s are often total junk. It was funny to use risky supplies when retro machines were $5 at goodwill, but I'm guessing your machine is worth a bit more than that to you, so just get something reliable. Its not bad practice at all to recap motherboards from that era from the get go either.

You can still find NOS power supplies for older AT style machines. Unfortunately startech appears to have discontinued their ps2power line, which were fairly decent imo, wish I had some spares. There are converters that will let you use a modern atx power supply with AT hardware though. Just ask if you get into such a project.

It is a worthwhile pursuit to learn how to maintain an old power supply however, if you're capable. I just dont recommend plug and pray on dusty old units.

Moral of the story:
Replace yo' caps.

Any electrolytic cap in excess of 20 years of age should be replaced with a modern low ESR capacitor from a reliable Japanese or US/EU producer like Panasonic, Rubycon, Chemi-Con, Sanyo, Vishay, Kemet, etc.

Oh, also, invest in a surge protector with a power switch so you can fully turn off everything from there. It can actually save you some cash over the years in lower energy costs too!

When people talk about the power supply taking out other components in a system, I have noticed that the most common scenario by far is the 5V standby line going rogue and blowing up something (motherboard/memory), which is what happened in your case.

Many people here think that using old AT power supplies is very risky, but IMO early ATX units are much, much worse due to the poor design/components of the standby line.

Anyway, I agree with the comments above: if you know how to refurbish old units (usually changing the fan and replacing capacitors is enough), then there should be no problem using those (assuming you stick to reputable brands), and remember to turn off the rocker switch on the back when not using the computer.

Otherwise, you can use modern PSUs, but there are some cases when these will not be enough (hungry Athlon XPs, multi-CPU setups and so on). You will probably also need to spend some extra bucks on adapters (SATA to Molex, ATX to AT and so on).

Personally, I prefer to get well built period correct units for very cheap (sometimes even NOS) and then I refurbish them properly.

Whether you buy new/old/period correct, and it doesn't matter whether it was today or buying new 20 years ago; the choice of a power supply is pretty much important as the motherboard itself. In fact, when you are building systems, you should learn how to read the specs of the power supply unit. But also, if you don't know how circuits work and detect signs for problems, you may be better off buying one that seems overspec'd from an reputable brand, spending some extra money. This is true today and it was 20 years ago. But of course, in old systems, the electrolytics are going to be an issue. So if you run these with any regularity, and want to not have to pour money down the drain, you probably should learn how to check them.

I don't know if you bought a unit that was NOS or used. Both can be equally bad. But I have some P2 workstations based on intel reference designs and early ATX power supplies, and the whole build thoroughly appears to be quality. I've had them for 20 years, run them periodically, and they still work fine. But it's hard to say if you can find these old quality systems, because they really do come from an era of cutting the cost of the components, like with the caps, you might have heard. I think it will be hard to pick up random stuff from the late 90's through 2000's ATX era. But who knows lately, since desktop systems are falling out of the market, and doesn't hold too much interest to me either. So again, unless you are willing to spend some money and searching, or learn refurbishing.

I don't have much of a fear for this, but I still leave every piece of vintage electronics plugged into a surge protector which I switch off when I'm not using it.

Granted, this is because some of my monitors and machines have bad power switches and will always run if power is applied at all, but still.

Always be careful with your vintage supplies, lads. Even reputable models can still have trouble, if you have a particular liking to a machine or a rare piece of equipment, maybe check the operation of the supplies monthly or recap and readjust them now before something bad happens. Best practice is to leave them unplugged, too.

DNSDies wrote:

Any electrolytic cap in excess of 20 years of age should be replaced with a modern low ESR capacitor from a reliable Japanese or US/EU producer like Panasonic, Rubycon, Chemi-Con, Sanyo, Vishay, Kemet, etc.

This does NOT go for everything. Capacitors are NOT always the issue, and changing the capacitors will NOT always repair a device. There are televisions out there from the 1950s with most of their original capacitors.

Granted, I will say that for digital electronics and computers, you really ought to replace them all outright. If you really care about the supply, you may also want to check separation in the transformer windings and you might even replace resistors / adjust the supply if you can. Electrolytic capacitors can often be very problematic in these devices.

Many of the early ATX supplies were cheap junk and then you have bad capacitors that came later. You should pop the cover of an old PS and look for bulging caps and then test the supply with a PS tester that has an LCD for voltages (under $10 shipped on ebay) before you use it with a vintage machine.

I still use old AT supplies that are as old as dirt with just a simple check with a multimeter on their output voltages. On early Athlon and P4 systems you need a supply that has a decent 5V capacity which newly made drives do not.

Capacitors from the 50s and 60s were formulated quite a bit differently -- and generally, they aren't trying to cram a bunch of stuff into a small metal box either. Electrolytics from the 80s and 90s are generally pretty good (before everything was "built to a price", and brands could still take pride in craftsmanship) but are getting to an age where nature is running its course. It's not a bad idea to replace them while they're still in good enough shape to NOT have done damage to anything. Caps of the 2000s are quite likely to be faulty and need to go just as a matter of course. Caps of the 2010s are probably just junk, so the product can be competitive with all the other $30 retail components on the market.

So, basically, if you didn't buy it new yesterday from a brand that specializes in bulletproof engineering, get in there and replace the caps! It'll probably double the cost you paid for it, but it's money well spent IMO.

FAMICOMASTER wrote:

This does NOT go for everything. Capacitors are NOT always the issue, and changing the capacitors will NOT always repair a device. There are televisions out there from the 1950s with most of their original capacitors.

I never said they were, but it's generally a good rule of thumb that old electrolytic caps should be replaced, even BEFORE problems start to appear if they're very old if you care about the longevity of your devices. Especially if they haven't been powered on for many years.
Electrolyte fluid can absolutely DESTROY PCBs and eat through traces. An ounce of prevention is sometimes worth a pound of cure.

Especially if they were made by a Taiwanese Company between 1999 and 2007, and they used that faulty electrolytic fluid recipe that got stolen...
https://en.wikipedia.org/wiki/Capacitor_plague

This sucks. BIG TIME. This is exactly why I've been considering installing a picoPSU into my childhood 27 y/o Compaq Prolinea 4/33. It's my first computer and would be heartbroken if it died because of something like this.

sorry to hear about that, unfortunately this happened. It's worth noting that not all power supply are created equal. I never even heard of Allied power supply's to be honest I they make shi**ty power supplys in 2019 also. New old has nothing to do with it.

I could be wrong but I thought Allied power supply were like the cheap power supply that came free with 30 dollar computer cases. 🤣

Allied = Deer. It was a period correct thing for the PSU to do that. 🙁

The only issue I've had with so called period correct psus is one Acorn A4000. i had a spare. Generally I power down my old systems when finished with them. When I get a new old system I generally clean them inside, inspect and do a soak test before putting it in to service.