With the development of electrostatic generators, air breakdown has become the main obstacle to further enhancing their output. Utilization of external circuitry to regulate the excited electric field strength in the generator's air gap for suppressing air breakdown is an effective approach. However, there is a lack of a standard metric for evaluating and optimizing its design. Here, we report a novel and standard metric utilizing plot to evaluate both the generator's output and upper limit, guiding its design under air breakdown limitation. Moreover, we introduce a concept of segmented tuning of the generator's gap electric field to expand the area of plot for enhancing the generators’ output. Integrated with the charge-excitation strategy, an ultrahigh charge density of 1.89 mC m⁻², energy density of 289 mJ m⁻² per cycle, and DC output power of 152 mW m⁻² Hz⁻¹ are all achieved at a 100 μm separation, capable of powering 20 portable calculators at 1 Hz. This study offers new insights to boost the electrostatic generators’ output under air breakdown limitation.