ozone kills smells pretty well, used for moldy car aircon etc

If you do open it up, have a good understanding of the charge capacitors can hold and general electrical safety.

I'm very scared of mold myself.
If I have any reason to believe the PC came from a mold infested house I won't take it.
Mold is always there it is impossible to remove mold from porous plastics and PCBs.
- They burn and get rid of every item from mold houses so mold spores won't repopulate again in fresh new built houses.

Ozone, Ionizers or such smell removers won't work. Only trashing and burning.
Get rid of: plastic items, wood=papers=books, fibers=clothes,...all porous materials exposed to mold.

Breathing mold makes your permanently allergic and sensitizes your smelling functions.
For example: some regular smells will start to smell permanently more if you are exposed to mold in history.

Umm no, a lot of things do kill mold and very effectively, one of which being ultraviolet from the sun. Vinegar, baking soda and peroxide also do.

Your post sounds a bit like hyperbole to be honest, but to be safe I will just order a new PSU, then open up and leave this out in the sun for a few days - I want to keep it because it has a strong 5V rail and -5V.

Indeed. Mold also can't magically 'infest' other houses. It needs damp, dark conditions to thrive. If you're worried about mold, ensure your house is dry, well-aired and exposed to sunlight regularly.

My other hobby is mushroom hunting, which brings me into contact with a lot of fungal spores. I can fortunately say that despite that I have no allergies to anything fungus-related, so I call BS on the claim that you get permanently allergic and your sense of smell get screwed if you breath in spores.

What is bad, is permanent exposure to mold (and damp itself). You don't want to live in conditions mold likes to live in. But that's not a mold problem, it's a housing quality issue.

In Finland. Mold inside public schools, hospitals and such is a real noted problem and causes permanent health hazards. It is not a joke.
When not affected yourself it is easy to be ignorant. Like cancer and such.
Mold has ruined a lot of lives.

Like I said, conditions where mold thrives are bad for your health, no doubting that. But that mold will not magially spread to dry, well-ventilated houses and it will not instantly cause allergy or other problems. For that you need long-term exposure. So it's not an issue where you source your hardware from, it's an issue where you live and store the hardware yourself.

I'd clean the PSU using vacuumer and brush, and wipe all internal and external surfaces with IPA.
Completely submerging and washing the thing in IPA helps a lot, too. (I have a 5 liter bottle for this, as the IPA can be reused often)
The MVOC sometimes creep into plastics, so usually it needs a while to evaporate the remaining smell.
For this reason get a new fan, they love to assume mold smell. The cabling might stink for a few weeks, until that dissipates, though.

As @dionb correctly says, the real issue is how you live and store your hardware.
Mold has some requirements to thrive, which are not given in healthy houses and storage facilities.

retardware wrote:

washing the thing in IPA

This would be my answer.

How about washing it with vinegar, followed by water, followed by drying in the sun?

Mold spores are everywere. It can come from everywere, like your hands or clothes or with the air when you open a window. Food can get moldy as well. Bread, jam and fruits. You just need the right conditions, that is all. An example of conditions can be some 70% air humidity. Mold can be bad, or usefull or even more usefull.

The thing is.... Don't be paranoid. Just keep the house dry, somewhat cool and well ventilated.

appiah4 wrote:

Umm no, a lot of things do kill mold and very effectively, one of which being ultraviolet from the sun. Vinegar, baking soda and peroxide also do.

Your post sounds a bit like hyperbole to be honest, but to be safe I will just order a new PSU, then open up and leave this out in the sun for a few days - I want to keep it because it has a strong 5V rail and -5V.

Or heat.... Mold will not survive temperatures over 85 degree celcius (185 degree fahrenheit).

appiah4 wrote:

How about washing it with vinegar, followed by water, followed by drying in the sun?

Should be fine but the big benefit of IPA is it evaporates quicker. I'd feel safer with IPA.
I would do the smoke test with hardware I didn't care about just to be safe as well.

PS
I open my PSU's somewhat often to dust. So I'd try simply leaving the sun opened up first and go from there

I've had some that smell bad. Take it apart, scrub the metal. I use vinegar and/or alcohol as well, and then clean with soapy water and an old toothbrush. If it's dirty I'll actually go ahead and wash / scrub the whole PCB as well -- with everything still on it. Usually then I would remove the caps and replace them with new ones. Definitely replace the fan -- that helps considerably. The wiring may smell, and if so, I'll replace it with donor cabling from a cheap PSU that I don't trust using, or just buy the connectors and some wire and make your own harnesses. (Sure is nice having the right plugs in the right places.)

user33331 wrote:

Ozone, Ionizers or such smell removers won't work.

Ozone doesnt remove the smell, it removes source of smell aka mold itself by binding oxygen atoms to everything

The smell you are complaining about is from the MVOC (microbial volatile organic compounds) that molds gas off.

These are very affine to plastics because the additives and softeners used in plastics also are mvoc-phile.
This is the reason why in particular plastics (i.e. fan, cables in our case) like to take the smell of moldy surroundings, even when they themselves have no mold growth.

While metals (at least those with non-porous surfaces) only carry the condensed mvocs on their surface and can be de-odorized easily by washing, these mvocs that have wandered into the plastics need to gas out to have the plastic become stink-free again.
So, if the smell is only light after washing, the remaining mvocs will probably disappear by themselves if the item is stored condensation-free with good ventilation.

I've washed out an ATX PSU in the sink with dishsoap before, you just need to dry it really well afterwards and let it sit for a few days to make sure there's no trace of water left.

Nprod wrote:

I've washed out an ATX PSU in the sink with dishsoap before, you just need to dry it really well afterwards and let it sit for a few days to make sure there's no trace of water left.

I did exactly this last night but without soap, just water. It's drying in the sun now. I will repeat with dishwasher soap tonight. 😀

You can also blow some compressed air on it after washing, water can get under capacitors and through-hole components andstay there a bit longer than normal.