Bi-directional control of power adapter and load

A system comprises a computer and an external power adapter configured to be connected to the computer to provide power to the computer. The computer comprises a computer control circuit that generates a computer control signal that is provided to the external power adapter and causes a change in an output voltage of the external power adapter. The external power adapter comprises an adapter control circuit that generates an adapter control signal that is provided to the computer and causes the computer to change its power draw. The computer and adapter control circuits generate the control signals on a common conductor interconnecting the computer and the external power adapter.