Modular dual power sources and corresponding systems include a common hybrid energy storage system, a high frequency DC-DC converter coupled between the common hybrid energy storage system, and an ultra-capacitor module for starting up a generator, and a two-level inverter coupled to the common hybrid energy storage system to provide power in case of an interruption in power supplied by a utility supply. The hybrid energy storage system includes an ultra-capacitor module and a battery module. A fast charger is coupled to the hybrid energy storage system to quickly charge the ultra-capacitor module and the battery module, which, in turn, charge the ultra-capacitor module for starting up a generator via a high frequency DC-DC converter. High frequency transformers are used to magnetically isolate electrical noise of the generator and UPS functions and operate independently. The modular dual power sources can be connected in parallel to provide large MW output power.