A host device can manage a controllable power adapter accessory using a communication protocol. Based on information provided by the controllable power adapter accessory as to its power capabilities and the power needs and preferences of the host device, the host device can determine a desired power profile and request power from the accessory conforming to the desired profile. The desired power profile can also depend in part on the power-carrying capability of one or more cables connected between the host device and the accessory. In some instances, the host device and controllable power adapter accessory can be connected via an intermediary accessory that can siphon power from the controllable power adapter accessory, and the host device can manage the power siphoning behavior of the intermediary accessory using the communication protocol.