Thanks for the reply I'm trying to reset everything to the way it was. My computer was off (nothing was running, led was off etc.) but my powersupply switch was in the on position and plugged into an outlet.
As long as your computer was off, you have nothing to worry about even if your PSU was in the 'on' position
Your PSU is made so it won't turn on unless it gets a signal from the motherboard.