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.