Thin relaxor-ferroelectric Pb0.9La0.1(Zr0.52Ti0.48)O3 (PLZT) films were deposited on Si substrates using Ca2Nb3O10 (CNOns) and Ti0.87O2 (TiOns) nanosheets as the growth template layer and SrRuO3 (SRO) as the base electrode layer, using pulsed laser deposition. XRD and cross-sectional SEM results show that the structure of the PLZT layers changes from very dense with (001)-orientation to columnar with (110)-orientation for CNOns and TiOns, respectively. The recoverable energy-storage density (Ureco) is nearly proportional to the critical electric breakdown field (EBD), which increases with PLZT film thickness. A very high Ureco value of 58.4 J cm-3 and energy-storage efficiency (η) of 81.2% were obtained at an EBD of 3400 kV cm-1 for the 1000 nm thick PLZT film on CNOns/Si, significantly higher than for the film on TiOns/Si (Ureco = 44.0 J cm-3 and η = 59.6% for EBD = 2800 kV cm-1). This excellent energy storage performance in the PLZT/SRO/CNOns/Si is due to the dense film structure and nearly hysteresis-free relaxor behavior. These results are important for improving the performance of relaxor-ferroelectric thin films for high-power capacitor applications.