Owing to surface modifications, triboelectric nanogenerators (TENGs) have seen increases in their electrical power and have successfully powered portable devices on their own. However, modifying the material and its surface may place limitations on the duration of device operation, and most of the portable applications demonstrated in previous studies have excessive input conditions. In this study, we developed a capacitor-integrated TENG (CI-TENG) that utilizes the fundamental mechanisms of the Leyden jar. The Leyden jar was the first form of capacitor that can store electrostatic charge and then discharge when two electrodes are sufficiently close for electrons to flow. In this device, a long sheet metal (capacitor electrode)–polymer–metal composite (TENG electrode) is rolled inside the casing cylinder, and a capacitor unit is fabricated at the end of the sheet composite. This is the first to integrate capacitor unit inside the TENG to generate higher ouput. This new operating mechanism of the CI-TENG is analyzed through the dielectric constant of the capacitor unit and the metal-to-metal contact between electrodes. Through the instantaneous charging and discharging of the capacitor unit inside the CI-TENG, it can generate a peak open-circuit voltage (VOC) of 156 V and a peak closed-circuit current (ICC) of 4.3 mA with a hand input. Compared with the conventional TENG, it charges a capacitor more than three times faster. Furthermore, the internal impedance of CI-TENG has shown to be decreased to 200 kΩ without any external circuit. The novel CI-TENG developed in this study provides a potential solution for CI-TENGs with a high-power output.