A series and parallel combined dual power system operates as a series combined power system, or as a parallel combined power system; the power from an engine directly drive the load; the system engages in the operation as the series combined power system incase of a light load; the load is driven by the engine in case of a normal load; an optional rechargeable device is adapted to the system; either or both of a primary and a secondary dynamo-electric units functions as a motor on the power from the rechargeable device to jointly drive the load with the power from the engine; and functions to provide power drive in case of a light load.