No, there's no switch. There's only the input plug with the normal three prongs, the wires that supply DC voltage to the computer and an on/off switch. Nothing else on the outside of the PS except the holes for the screws to attach it to the case.

When I switch it on, the fan doesn't even come on. I know it's not much to go on. I suppose I need to start unplugging cables out of the PS to see if any of them have DC but if the fan doesn't work, then what's the use.