As increasing power requirement in more or all electric aircraft, electric power system is required to be more efficient and lower in weight. Among the current power generation technologies, 115V variable frequency (VF) system and 270VDC system are regarded as the two optimal options for future use in MEA or AEA. Therefore, it is very important to compare their relative merits in order to determine the optimal choice on the primary power type. As the reviewed literature mainly represents the comparison between 270VDC system and 115V constant frequency system, it is very necessary to conduct the comparison between 270VDC system and 115V/VF system. The aim of this study is to grasp the nature of these systems and evaluate these two systems in terms of some engineering aspects. Literature regarding the power generation technology is first investigated. Based on initial comparison, the 270VDC brushless generating system and 115V VF generating system are selected for this study. Before conducting system architecture design and wiring system design, the load requirement analysis and optimization are conducted. Finally, a comparison between these two systems will be made in terms of weight, power off take, minimum voltampere (VA) capacity requirement, voltage drop, reliability, life cycle cost and risk. The results show that the 270VDC system is superior to the115V/VF system in terms of weight and efficiency. With regards to system reliability, the 270VDC system can be designed as either an active parallel system or a standby system while the 115V/VF system can only be designed as a standby redundant system. As far as risk is concerned, the 270VDC is more dangerous than the 115V/VF system in terms of arcing risk and corona discharge. All in all, the 270VDC system can be considered as the optimal choice for future use in AEA or MEA.