Improving the output energy is critical for the wide application of triboelectric nanogenerators (TENGs), in which increasing the surface charge density is an effective approach. However, when the surface charge density increases to a certain value, air breakdown will occur and become the main obstacle to the further improvement of the output energy. Herein, we report a strategy to retard air breakdown and enhance the output energy for contact-separation mode TENG by utilizing a tailored external capacitor and multilayer structure with a small air gap in each layer. Based on this strategy, we establish a compact TENG (2cm × 2cm × 2mm, at separation) with an ultrahigh output energy density of 177.8Jm-3cycle-1(13 times elevation than a conventional one), which is a new record. Combining with a passive power management circuit, the stored energy of 118.5Jm-3cycle-1and average power density of 107.9Wm-3at 1Hz are achieved (350 times elevation than a conventional one). The compact TENG can continuously drive various portable electronics at 1Hz excitation. Our research greatly promotes TENG toward practical applications