Methods of and apparatus for controlling power drawn by an appliance through a USB port. The method includes limiting any electrical current drawn by an appliance to one of seven levels according to whether the data lines receive a bias from a power line, the data lines are in electrical communication with each other, and the power source includes a host computing device, or according to logic and voltage levels of the data lines when any of the pull-down resistor and the current and voltage sources are connected or not connected to the D+ data line. The apparatus includes a controller programmed to selectively connect a pull-down resistor, a current source, and a voltage source to a D+ data line and to limit any electrical current drawn from a power source to one of the seven levels according to voltage levels on the D+ data line and a D− data line.