the present disclosure relates to a power supply device for hybrid construction machinery , and more particularly , to a power supply device for hybrid construction machinery , which is capable of reducing engine loads and facilitating improvement of engine efficiency by excluding a starting motor used in general hybrid construction machinery and an alternator for charging a battery from hybrid construction machinery , such as a hybrid excavator or vehicle , which commonly uses an engine and an electric motor as a power source and includes an electric energy storage device , and a method for the same .