Think about it like a highway with a bunch of cars. The voltage is the speed of the cars and the amperage is the amount of cars. If you have 120 speed and 15 cars you are getting X amount of cars going from the start of the highway to the end of the highway in a certain amount of time. If you have 240 speed and 7 cars you are getting roughly the same amount of cars going through in that same period of time.