|Please clarify. Supply voltage is what (US 110V, Euro 220V)? |
Moving switch to 220V and using it on 110V supply (US), especially if moved when power was off, will probably have no permanent effect since you would get a low voltage at the outputs and you would just not be able to boot.
The opposite, where you used 110V setting on 220V supply (Euro) will send higher voltages out of the transformer and into the filtering circuits and probably cause damage to the power supply. The two things that are not clear is whether there is a cut out circuit that could have protected the power supply, and whether any higher voltages got through to computer components (really bad).
At this point, you can remove the power supply, look up the correct voltages at each connector and use a voltage meter to see if it is working correctly. If it is, try it in the machine to see if there is damage there (or borrow another power supply to test it). You could however, take the risk of just trying the power supply, assuming that any damage is probably already done, but that would be your call.
You have to be a little bit crazy to keep you from going insane.