Electric power is the cornerstone of economic growth, as well as one of the major energy sources for modern society. Economic growth, the demand for electricity, the security of fuel supplies, power-generating technologies, and the impact on the environment must be considered in the development planning and policy making of electric power. In fact, the planning of electric power development and the establishment of power generation capacity are complex and dynamic processes, which are influenced by national policies, citizens' acceptance, and domestic and international energy sources. Hence, this study adopted system dynamics methodology to explore the development of policy-based electric power planning in Taiwan, analyzed its system structure, and simulated the impact of energy source policies on Taiwan's power supply according to different scenarios of economic growth. The findings of this study showed that the power supply in Taiwan is mainly influenced by four subsystems with three important level variables, including the installed capacity of thermal power, installed capacity of nuclear power, and installed capacity of renewable energy. Currently, Taiwan plans to eradicate nuclear power by 2025 and replace it with renewable energies, which could result in power shortages and power rationing.