A surgical instrument comprising: a housing that comprises a handle configured to be grasped, manipulated and actuated by a clinician; an interchangeable shaft assembly having a surgical end effector operably coupled thereto that is configured to perform one or more surgical tasks or procedures, wherein the housing is configured for operable attachment to the interchangeable shaft assembly; wherein the housing comprises: a main power supply circuit configured to supply electrical power to a primary circuit; and a supplementary power supply circuit; wherein the interchangeable shaft assembly comprises a secondary circuit; and wherein the supplementary power supply circuit is configured to supply electrical power to the secondary circuit; and an over current/voltage protection circuit (7012, 7030) coupled between the main power supply circuit and the supplementary power supply circuit or incorporated into the supplementary power supply circuit, wherein the over current/voltage protection circuit (7012, 7030) is configured to isolate current from the main power supply circuit to the secondary circuit when the supplementary power supply circuit experiences higher levels of current or voltage than expected. a housing that comprises a handle configured to be grasped, manipulated and actuated by a clinician; an interchangeable shaft assembly having a surgical end effector operably coupled thereto that is configured to perform one or more surgical tasks or procedures, wherein the housing is configured for operable attachment to the interchangeable shaft assembly; wherein the housing comprises: a main power supply circuit configured to supply electrical power to a primary circuit; and a supplementary power supply circuit; wherein the interchangeable shaft assembly comprises a secondary circuit; and wherein the supplementary power supply circuit is configured to supply electrical power to the secondary circuit; and an over current/voltage protection circuit (7012, 7030) coupled between the main power supply circuit and the supplementary power supply circuit or incorporated into the supplementary power supply circuit, wherein the over current/voltage protection circuit (7012, 7030) is configured to isolate current from the main power supply circuit to the secondary circuit when the supplementary power supply circuit experiences higher levels of current or voltage than expected. a main power supply circuit configured to supply electrical power to a primary circuit; and a supplementary power supply circuit; wherein the interchangeable shaft assembly comprises a secondary circuit; and wherein the supplementary power supply circuit is configured to supply electrical power to the secondary circuit; and an over current/voltage protection circuit (7012, 7030) coupled between the main power supply circuit and the supplementary power supply circuit or incorporated into the supplementary power supply circuit, wherein the over current/voltage protection circuit (7012, 7030) is configured to isolate current from the main power supply circuit to the secondary circuit when the supplementary power supply circuit experiences higher levels of current or voltage than expected.