Hmm.. I've always assumed that a circuit will have a source voltage.. determined by the voltage of batteries used, or the voltage of the wall outlet... And based on this voltage, the circuit will draw the amount of current that it needs based on the resistance, reactance, etc. of the combined total of all components of the circuit. More resistance, more amps. As long as the power source can provide the amperage being drawn, there's no issues. If the power supply is capable of providing more current, it won't just put more current into the circuit... it only provides the amount of current that the circuit draws, or "asks politely for".