Could be the dust burning, I'd suggest you treat it with some compressed air or a brush to clean it up. Preferably both (air, brush, air again).
Also, are you sure it was the PSU that gave the smell? Look for any vented caps on the mobo, and if it has any tantalum capacitors (or any of the add-on cards have them) inspect those as well.

It was fairly clean but I'll clean it anyway. I only have this PSU, no other parts of the original PC.
As you can see there is that white glue everywhere they used to keep the parts in place. That could be the culprit, I don't know.
Everything else seems intact and the smell is so strong that it's impossible to find the source.
When I tested it the temperature was fine, barely warm to the touch. Strange.

Oh, I misunderstood, I thought you tested it with a mobo you already had.

Well, it looks OK-ish, nothing obviously wrong with it other than being old PSU. Even the line noise suppresion parts are all there so it's not the cheapest variant that could be made. Maybe it just has that kind of smell, or maybe it was in a machine that blew a cap and the fan sucked all that in through the PSU. I wouldn't worry if it works and nothing bad happens, these rarely die slowly so you'll know when it goes 😀 Also, the glue is fine and I've seen it used, shouldn't have any smell to it.

Other than the smell it's completely fine so I'll just clean it and air it out, not much else I can do. Thanks.

You could also dunk it in a water bath with a bit of dish detergent added, and scrub it (gently) with a soft brush. I pretty much wash all my PCBs, I don't deal with tobacco smoke residue well. Obviously let it sit a few days in room temperature to properly dry after that. And don't put it in water right after powering off, let the caps discharge (10 minutes will do). The metal case can be washed too, but that has to be dried with a towel quickly after or it'll start to rust.

Not everything can be washed in water, even disassembled, but PSUs can be. I've yet to damage anything by doing that.

Same. Most AT supplies I get have seen a few years of service, so I decap them, bathe them and scrub them with a toothbrush under running water, dry for a day or maybe two (it's very dry here), then re-cap, re-assemble, test with a dummy load, and back into service it goes.

I avoid washing the transformers. Remove them, the PFC inductor (if present), wash the rest. I clean those as good as I can without bathing them. If water gets between the windings it could take much more than a few days to dry out completely.
One exception had to be made, the whole PSU was too filthy. Works OK, but I left it for months after washing it.

Your PSU looks OK. Just make sure the fan works, else it will overheat-smell-destroy itself.

Bear in mind, those trafos have lacquer-coated copper wire, often sealed in tape. If water gets in to the tape after a brief washing, it should be able to get back out easily enough. If it's in there good, well.... it's coated wire. It has to be, otherwise, it would just be a spool of short-circuit.

To each their own, and climate plays a part for sure. Just food for thought.

Thanks for the replies. Are detergents like baking soda or vinegar safe to use? That's probably the only thing that gets this smell out.
I left it outside for the night to air it out but the smell is the same so I need something more effective.
I'll dry it on the radiator for a few days.

Safe? No, these are aggresive chemicals, but no so much that short-duration dunk, followed by a good rinse would be a problem. Just don't let the PCB sit in it. Personally I'd say vinegar smell is not a big improvement over the "dirty electronics" one. Maybe try water with detergent first (and remember to scrub) and see/smell what comes out of it after it dries? You can repeat that process after all, if necessary.

You may just have to run it for a while. My whole retro fleet is pretty recent, having only gotten back into this not quite a couple years ago. Almost all of the stuff I have now is re-purchased used from eBay, with a couple select local pickup items. Many of the cases and PSUs have "a smell" of their former life. The ones that I use more don't smell like anything anymore. Some of the ones that don't get used too often produce an aroma when powered on. Luckily, the worst offenders (musty basement smell, mostly) cleaned up well with some soap. The ones that still have a fragrance about them don't smell bad per se. It's just the smell of someone else's house or whatever.

IBMFan wrote on 2020-03-04, 17:40:

Hello […]
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Hello

I have a Hipro HP-M1554F3P (IBM 00NN7687) power supply I got for free.
The moment it arrived I noticed that it smells like it was rescued from fire. The usual electronic burn. I tested it anyway and it runs stable. I tested voltages under load, all good.
I opened it to find the burned parts but found nothing. No burns on the component side, nothing on the solder side. It was never opened before, the warranty seal was intact. So what could be the source of that smell? I suspect one of the transformers from a previous overload (mainly the one with the Danger sign) but can't confirm.
What are your thoughts?

Maybe the motherboard or another component cooked up and fumigated the PSU?

I managed to get another PSU of the exact same model so I decided to go "all the way" on this one.
First I washed it under water and scrubbed the panel with a toothbrush. Applied a little dish detergent too. It didn't do much in regard to the smell so I took it completely apart and dunked each part in 20% vinegar for an hour.
After that I washed everything again for a few minutes and dried it for 2 days on the radiator.
It looks like new, no corrosion of any kind but the smell is still there! Not that strong but it's definitely noticeable.
The PSU works like a charm but I failed to get the smell out.
It seems that burnt plastic smell is nearly impossible to get rid of even when I do crazy things with it. Or it needs way more time in the vinegar bath.
Maybe if I dunked it in perfume... but it would probably smell like burnt plastic AND perfume forever.
On the other hand it was a great way to debunk a few myths.

Short-term water and vinegar exposure has no corrosive effect on any of the panels, parts or the PSU case (ON THIS MODEL).
All labels have to be removed beforehand.
It doesn't take 1-2 weeks to dry the PSU like a few websites mentioned, it took 2 days at most on a radiator. I'm almost certain that 1 day would have been enough but I wanted to make sure.
Vinegar smells bad but it doesn't actually remove other bad smells like I expected. It just adds to the bad smell that you have to get rid of under running water. It helped but the extra work/risk was NOT worth it.

We should come up with a safe mix to get rid of strong smells without damaging the parts and circuits.

Thanks for all the suggestions.

I use plain old white vinegar to clean some things. It's good for removing battery acid, for example. It smells a bit when you apply it, but it also washes off really easily. I use it in laundry sometimes too, and you can't tell after the wash. I don't think you would add a vinegar smell long-term by using it. 😀

I'll often clean things with rubbing alcohol if there's flux residue, some kind of varnish on the PCB that is sticky and nasty to work on, or to get rid of smells, marker stains, residue (adhesive residue often needs something like Goo Gone)... It doesn't always remove smells, sometimes you just have to let it gas those off naturally.

Final rinse should be 99% alcohol that you can get from drug store this will get the water diluted quick and speed up drying process. I do this all the time at work for rescuing wet phones by extracting the board, strip the covers off, then put boards through ultrasonic cleaner fluid in the ultrasonic cleaner machine for 3 minutes. Then rinsed off in hot water tap then dunked and swished in the tray of alcohol for few minutes. Dry off excess with paper towel.

Then in the warm air circulating special oven around 60C for half hour. Mainly to speed up the drying process. You can use hair dryer after alcohol rinse, smell the board to know if alcohol is all evaporated, then you have a dry board once again.

BUT, please wait a day or two with power supply board to dry completely in warm place after that. Just in case.

Cheers,