It is essential to secure energy sources by installing a private power generator for business continuity in a power outage. The authors have developed an optimization tool to estimate the optimal amount of distributed power supply equipment using economic efficiency and resilience as two evaluation indicators. However, it is questionable whether the private generator in a hospital building can generate sufficient electricity to meet demands in case of a power failure, because demand has short cycle fluctuations on the order of seconds, and the private generator must respond to these fluctuations from time to time in the case of stand-alone operation. The optimization tools we have developed in the past have not considered the balance between power output and load demand (demand sufficiency). Therefore, this paper proposes a new optimization method that considers balancing power supply and demand in private generators’ independent operation during power outages. We narrowed the optimization constraints as demand sufficiency conditions: standard AC frequency range between 49 and 51 Hz. More practical optimal solutions are obtained by applying the new constraints to the multi-optimization. We also compare the case study results by applying these constraints to the results of previous case studies.