A wired connection, such as USB-C, for charging a sink from a source, has a configuration channel and a power transmission channel. The presence of data on the configuration channel is used to determine that a cable has been disconnected from the power source. This charging system contains a capacitive power converter and a controller for controlling the capacitive power converter. There is also a configuration channel detector, which is arranged to detect the status of the configuration channel and to provide this status to the controller, so that the system can determine that the source has been detached from the bus when no configuration channel data is present.