In the work, we successfully fabricate mesoporous N- and O-enriched carbon (NOC) with adjustable porosity and specific surface area (SSA) by using low-cost lignite as a precursor coupled with general KOH or ZnCl₂ activation for electrochemical capacitors (ECs). Physicochemical and electrochemical characterizations reveal that chemical activating agents influence significantly upon the specific morphology, pore structure, and electrochemical performance of the resultant products. Strikingly, KOH-activated NOC (NOC-K) sheets are endowed with high SSA of ∼1257 m² g⁻¹, large pore volume of 1.3 cm³ g⁻¹, and optimized pore size of ∼3 nm, rendering its electrochemical capacitance superior to those of NOC and ZnCl₂-activated NOC (NOC-Z) in 6 M KOH. Thanks to its rich mesoporosity coupled with large electroactive SSA and heteroatom doping (N of ∼4.8 at.% and O of ∼23.3 at.%) effect, the NOC-K electrode yields even better electrochemical behaviors in 1 M H₂SO₄ than those in 6 M KOH.