A direct current triboelectric nanogenerator (DC-TENG) utilized the air-breakdown effect to collect triboelectrification charges from dielectric tribo-layers, providing a new type of mechanical energy harvesting mode for TENGs, and demonstrating its high efficiency in the energy conversion process. However, boosting the output performance based on structure designs and material modifications still faces great challenges. Herein, we propose a ternary dual-DC-TENG (TDD-TENG) with a triple synergistic enhancement mechanism. The strategies include space optimization using a multiple-unit structure on a slider by seamlessly arranging a PTFE/PA/electrode to realize maximized space utilization, ternary dielectric material selection by adopting PTFE, PA and PU foam as the tribo-layers with the spontaneously introduced PTFE powder on PU foam to achieve a higher triboelectrification effect and surface lubrication, and a bottom electrode design to collect charges unreached by charge collection electrodes (CCEs) on the slider forming a dual-DC output. Consequently, TDD-TENG achieves an average power density of 18.37 W m−2, which is the highest in sliding mode DC-TENGs. In addition, the output charge density of the rotary TDD-TENG reaches 7.3 mC m−2 at an ultra-low speed of 5 rpm. This work provides a new method to improve output power through structure design and material modification for DC-TENGs.