Anyone care to explain? In layman's terms?

Well, my laymans understanding is that the power must be regulated within the player. A car is going to put out a wide range of power (probably anywhere from 9V to 16V) while being started, using headlights, accessories, etc. which the player must compensate for. That same regulator gives us leeway on which power supplies we can use and as tanstafl mentioned the amperage is irrelevant as long as it is sufficient.

-Mike