HYDRAULIC POWER SUPPLY UNITS WHICH CIRCULATE AND REGULATE THE FLOW OF FLUIDS IN A HYDRAULIC SYSTEM; AND HYDRAULIC SYSTEM; AND HYDRAULIC CONTROL SYSTEMS COMPRISED OF HYDRAULIC SERVO VALVES, SERVO ACTUATORS, AND OTHER CIRCUIT COMPONENTS WITH THE COMBINATION THEREOF PRODUCING A RESULTING FORCE, A FORCE THAT MAY INTERACT WITH AN INPUT OR REFERENCE FUNCTION