Supercapacitors have been considered as a promising alternative of aluminum electrolytic capacitors (AECs) for AC line filtering applications. However, realizing supercapacitors with fast frequency response and superior energy density still remains an open issue. Herein, we demonstrate a hierarchical, vertically‐oriented carbon nanowall foam (CWF) supercapacitor using mixed room temperature ionic liquids (RTILs) for high‐performance AC line filtering. Hierarchical CWF exhibits macrospores as electrolyte reservoirs to shorten ion transport distance, vertically‐oriented, open channels to enable fast ion diffusion and consecutive scaffolds to promote electron transfer. CWF supercapacitor using RTIL mixture realizes a recorded‐high areal energy density of 1.23 μWh cm−2 at 120 Hz (almost ∼2.0 times/∼10.0 times larger than those of organic/aqueous electrolytes, respectively) and fast frequency response (RC time constant=∼1.3 ms). More importantly, CWF supercapacitor achieves a capacitance advantage over commercial AECs up to 1,000 V, substantially larger than those reported in state‐of‐the‐art literatures (maximum of ∼250 V).