How do I read my AC Adapter label.
For worrying about the circuit breaker limit it is the 2.5 amp rating that matters.  Thats the maximum amperage it will draw at 120V.  Typically it will draw significantly less than that.

The total power is Volts * Amps.  Which is why the lower voltage output can provide more current.  The total power coming in and going out stays the same, minus the inefficiencies of the power brick itself.