Abstract: Starting from the long-existing engineering and technical challenges in three types of rail transit traction power supply systems—DC(urban rail) power supply, AC(railway) low-frequency co-phase power supply (i.e. COPPS), and industrial-frequency single-phase cyclic connection power supply, the technological advances are reviewed and summarized in these systems, mainly on the view of the application of power electronics in this field. Crucial developments are reviewed and categorized, including: track potential and stray current corrosion management, regenerative braking energy recovery in DC power supply systems; upgrades and improvements in 3→1 phase frequency conversion units, and power electronic traction transformers in low-frequency co-phase power supply systems; section transition technologies for locomotives, power quality compensation, COPPS and virtual co-phase power supply (i.e. V-COPPS), locomotive-grid coupling oscillation suppression, as well as the integration of green energy into rail transit traction power supply systems. Based on these insights, reflections on the future development of DC and AC traction power supply technologies are presented, respectively, from the demands for environmental sustainability, low energy consumption, high efficiency, safety, reliability, and long-term global sustainability.