For large power DC loads such as data centers, EV charging stations, light rail, etc., the medium-voltage-connected power supply is promising since it eliminates utility-frequency transformers, reduces power conversion stages and distribution loss and has a smaller size. In this paper, the front-end AC/DC conversion stage of the medium-voltage-connected power supply is investigated. Five AC/DC converter circuits are compared with respect to the efficiency and the power density by optimizing the switching frequency, the filter inductor and the heat sink.