Or just go with an electric duster. Its air and no water!
Remember that the other 30% of a Ispropyl 70% alchohol is made up of water.
Tap water = water with minerals. Minerals = Conductive.
Distilled water = Water with no minerals. Doesn't necessarily mean its safe to use either.
Even tap or distilled water, I highly disagree washing your PSU with water as mentioned in the post above me.
If you did went ahead and wash it with water, make sure its COMPLETELY dry or else you greet the magic smoke!
Effect of distilled water on electronics
View: https://www.youtube.com/watch?v=qGbQ2FPDqkw
And true, remember that capacitors can hold a charge for a VERY LONG time. It doesn't necessarily mean when you turn off your PC/PSU, that the capacitors are discharged. This is the reason why its not advised to open a PSU and poke around with your finger touching things inside.