This article presents the development and performance of ultrahigh-power micrometre-sized supercapacitors based on onion-like carbon (OLC). The authors demonstrate that these microsupercapacitors can achieve power densities comparable to electrolytic capacitors, capacitances four orders of magnitude higher, and energy densities an order of magnitude higher. The microsupercapacitors were produced using electrophoretic deposition of OLC onto interdigital gold current collectors, resulting in a high surface-to-volume ratio and improved performance due to the ease of ion access. The microdevice was tested at scan rates up to 200 V s\(^{-1}\), which is three orders of magnitude higher than conventional supercapacitors. The specific capacitance of the microdevice was 0.9 mF cm\(^{-2}\) at 100 V s\(^{-1}\), and the device exhibited a very low relaxation time constant of 26 ms, indicating fast ion accessibility. The OLC-based microsupercapacitor outperformed other energy storage devices, including electrolytic capacitors and conventional supercapacitors, in terms of power and energy density. This work addresses the need for microscale energy storage in applications such as nomad electronics, wireless sensor networks, and biomedical implants.This article presents the development and performance of ultrahigh-power micrometre-sized supercapacitors based on onion-like carbon (OLC). The authors demonstrate that these microsupercapacitors can achieve power densities comparable to electrolytic capacitors, capacitances four orders of magnitude higher, and energy densities an order of magnitude higher. The microsupercapacitors were produced using electrophoretic deposition of OLC onto interdigital gold current collectors, resulting in a high surface-to-volume ratio and improved performance due to the ease of ion access. The microdevice was tested at scan rates up to 200 V s\(^{-1}\), which is three orders of magnitude higher than conventional supercapacitors. The specific capacitance of the microdevice was 0.9 mF cm\(^{-2}\) at 100 V s\(^{-1}\), and the device exhibited a very low relaxation time constant of 26 ms, indicating fast ion accessibility. The OLC-based microsupercapacitor outperformed other energy storage devices, including electrolytic capacitors and conventional supercapacitors, in terms of power and energy density. This work addresses the need for microscale energy storage in applications such as nomad electronics, wireless sensor networks, and biomedical implants.