Two electrical sources for one load
This is a power grid (or microgrid) function. It requires the two source voltages to be matched and also the frequency and phase if they are AC sources. Once matched, the sources can be paralleled. Each source must have a current control or generator excitation control system that limits the amount of power that is dispatched. There must be a supervisory control system and likely a human interface system that decides how much power to dispatch from each source under specified circumstances. Appropriate measures must be taken to protect the sources and to maintain system stability. That is a general outline of the system required. Evaluating the alternative design approaches and implementing a design is too broad a subject to be covered here.