Enhancing the efficiency in energy storage capacitors minimizes energy dissipation and improves device durability. A new efficiency-enhancement strategy for antiferroelectric ceramics, imposing relaxor characteristics through forming solid solutions with relaxor compounds, is demonstrated in the present work. Using the classic antiferroelectric (Pb0.97La0.02)(Zr1-x-ySnxTiy)O3 as model base compositions, Bi(Zn2/3Nb1/3)O3 is found to be most effective in producing the “relaxor antiferroelectric” behavior and minimizing the electric hysteresis. Specifically, a remarkable energy storage efficiency of 95.6% (with an energy density of 2.19 J/cm3 at 115 kV/cm) is achieved in the solid solution 0.90(Pb0.97La0.02)(Zr0.65Sn0.30Ti0.05)O3–0.10Bi(Zn2/3Nb1/3)O3. The validated new strategy, hence, can guide the design of future relaxor antiferroelectric dielectrics for next generation energy storage capacitors.