A keyed power source connector (32) and keyed device connector (14) that are backwards compatible, ensuring that the power rated device connectors can only mate with power source connectors power rated at or above the device connector power rating. One connector is formed as a plug, and the other connector is formed as a socket. The connectors have peripheral contoured body portions (16, 34) having a profile being a function of the respective connector power rating. A keyed portion (41, 62, 72, 82) of the power source connector plug will physically interfere with and not be receivable within a device connector socket when the device connector power rating exceeds the power source connector power rating. This connector system (10) ensures target portable electronic devices coupled to the device connector can not draw power exceeding the rating of the power source connector.