A power system and method for the adaptive power control of a drilling rig. While operating the internal combustion engine in its efficient operating range, unrequired mechanical power is converted to electrical power for storage, or use via the electrical bus on the rig. When the internal combustion engine is not required to provide mechanical or electrical power it is deactivated, and then reactivated—electrical storage on the system in the meantime providing electrical power to the bus as required. The power supply and management system could be retroactively fitted to an existing drilling rig by the incorporation of a generator and electrical storage device thereon. The system and method of the present invention allow for the optimized use of combustion-based power on a drilling rig while minimizing environmental emissions from the idle running of the at least one internal combustion engine.