1. A method implemented by a host computing device comprising: detecting connection of an accessory device to the host computing device via an accessory interface; obtaining data indicative of an identity of the accessory device; determining based on the data indicative of the identity whether the accessory device is an authorized accessory; and when the accessory device is an authorized accessory, setting a default power contract for power exchange with the accessory device established based on the identity, including: looking-up power contract settings associated with the accessory device; and setting a power exchange direction and current limits according to the power contract settings;