Dynamic and steady-state averaged models of an aircraft's power systems are developed to better understand various aspects of operation such as coupling between energy domains, energy requirements, transient and fault conditions/recovery, power quality/reliability, system and subsystem-level losses, operational efficiency, and to explore numerous system architectures. These models focus on the electrical, thermal, hydraulic, mechanical, and pneumatic power systems traditionally found in commercial aircraft. Subsystems of components are capable of interfacing with each other and with an engine model that produces auxiliary power. One of the major challenges involved in modeling extensive systems of this nature is to arrive at an optimum trade-off between simulation execution time and the desired level of fidelity in the result. In this work, relatively crucial components involved in the operation of an aircraft's systems such as the engine generator unit, batteries, air-cycle machine, and the cabin/cockpit are modeled incorporating dynamic behavior, while other components are represented by steady-state averaged models or operational maps. Individual loss models are incorporated in many components to capture and understand the strong coupling between power domains due to efficiency losses. The developed generic models are easily scalable to various power levels and aircraft configurations. Also, the model seamlessly allows addition of new components to the existing system and evaluation of their impact on the existing system stability. The developed component models are assembled into a representative aircraft model and the operational aspects are studied by simulating typical mission envelopes.