Closed-Brayton-cycle (CBC) is a potential onboard power generation technology for hypersonic vehicles, but finite cold source limits its power output. To achieve higher electric power, this study presents the power optimization and comparison between the simple recuperated and recompressing supercritical carbon dioxide (S-CO2) CBC Results indicate that the temperature distribution of precooler is essential to obtain its pinch point temperature difference. There is optimal fuel temperature difference in precooler for electric power of S-CO2 CBCs. Although the recompressing layout has advantages on thermal efficiency, the simple recuperated layout exhibits better on electric power per unit mass flowrate of fuel (219.6 kW vs. 192.5 kW), because the latter utilizes more cooling capacity of fuel. Besides, the optimal inlet temperature of compressor for electric power with finite cold source is far higher than the design value for general S-CO2 compressors (389 K vs. similar to 305 K). In a word, it is more reasonable to develop the simple recuperated S-CO2 closed-Brayton-cycle as onboard power generation system of hypersonic vehicles. (C) 2019 Elsevier Ltd. All rights reserved.