Cleaning psu

Compressed air is completely safe. If you detect any moisture in it then let the computer dry for an hour or so before you power it on. Keep in mind there is a ton of moisture in the air... Sometimes there is enough moisture in the air that water actually falls from the sky! Point is a little moisture is ok.

I have been cleaning computers with a heavy compressor for 10 years, never had an issue.

Washing a psu in the tub with shampoo is idiotic. Can you do it safely if you want to spend hours and hours? = yes. Does it make sense? = No
Just use air.

Years ago my wife spilled an entire cup of coffee on her laptop. It was a full 12-16 ounces. So I took the entire computer apart and washed the ram and mother board in a hot water bath. I then used compress air to dry it followed by 30 minutes in the oven set to 150. That laptop still works today. This was a laptop that would not work, so we had nothing to lose. Doing this on a working component does not seem wise.
 
I would not, unless I was really bored. I do dumb things when im bored.

It can be done safely.... question is how long do you need to leave a psu in the sun to get it completely dry before it is safe to use again? If there is water shorting across the 12 volt and 5 volt rails this could destroy all the components in the computer.

Why do you need to clean it with soap and water? Did you get drunk and pee on it or something?
 
When I worked in a retail shop we had a moisture filter on our compressor that had a little, about 2 ounce, reservoir. We only had to empty it about twice a year. Cans of compressed air don't have water at all. They have a non-conductive, fast evaporating substance in them that is really cold if you hold the can upside down and spray it at a noob.