Nitrogen and sulfur co-doped porous carbon (NSCDPC) was prepared using a one-step method using a purple-leaf plum kernel shell, potassium benzoate, and N,N′-diphenylthiourea (DPTU) as the carbon precursor, the activator and the nitrogen and sulfur source, respectively. The use of potassium benzoate with weak alkalinity and causticity facilitates obtaining abundant microporous structures and heteroatoms. Meanwhile, the dopant N,N′-diphenylthiourea plays a synergic activation role. The optimal layer-stacked NSCDPC_750-1 exhibits abundant ultramicropores and defect sites, developed interconnected channels, a large specific surface area, and rich nitrogen and sulfur contents, resulting in excellent electrochemical performance. As expected, NSCDPC_750-1 exhibits a high specific capacitance of 338 F g⁻¹ at 0.5 A g⁻¹ in 6 M KOH electrolyte, an outstanding rate performance with 280 F g⁻¹ at 20 A g⁻¹, and remarkable durability with 92.3% retention after 10 000 cycles. In addition, a symmetric supercapacitor assembled with NSCDPC_750-1 as the electrode and 6 M KOH as the electrolyte possesses an outstanding specific capacitance of 111 F g⁻¹ at 0.5 A g⁻¹, an excellent rate capability, and a high energy density of 30.22 W h kg⁻¹. The impressive electrochemical performance makes NSCDPC_750-1 a promising supercapacitor electrode material.