Hi,
This is a question i hear quite a bit, especially when the power supply is marked on the case something like "12 volts, 1 amp". People ask, "How can it be putting out 1 amp when i havent even connected anything to it yet?"
The answer is, the 12v is the voltage it can output and it can output that voltage up to and including 1 amp, but not over 1 amp. Thus it will work with loads that draw less than or equal to 1 amp. With no load connected it outputs zero amps.