Pedal power supply question

Your fine. You have 15 AMPs in your wall socket too but you only use a tiny bit of that when you plug in the Power supply. 
Most important is a steady clean voltage which should be regulated in a quality supply. That's why it's not recommended to use cheap generic power supplies, they are never regulated. 
The pedal will just use what it needs. The reason it has a high output is so it can power up more than one pedal.