This work demonstrates the best piezoelectric energy harvesting performance of highly flexible nanofiber-based composite nanogenerators with very promising charging capability. The exceptional selection of high piezoelectric coefficient Pb(Zn_1/3Nb_2/3)O₃–Pb(Zr_0.5Ti_0.5)O₃ (PZN-PZT) nanoparticles enables the nanogenerators to be very competitive. It covers the entire procedure of fabricating the energy harvesters, i.e., (i) finding optimal composition in the system of PZN-PZT, (ii) synthesising nanoparticles by combustion reaction, (iii) treating surface of the nanoparticles, (iv) producing nanoparticle-dispersed composite nanofibers, (v) fabricating nanogenerators, and (iv) suggesting the enhanced way of charging capability by designing electrical connections. The achieved harvesting performance of ~3.4 V and ~240 nA is the best one so far for the nanofiber-based piezoelectric energy harvesters. The promising result is possible by adopting the optimal composition of 0.4Pb(Zn_1/3Nb_2/3)O₃–0.6Pb(Zr_0.5Ti_0.5)O₃, which is far better than pure PZT in terms of piezoelectric properties. Composite nanofiber sheets consisting of uniformly distributed nanoparticles in the P(VDF-TrFE) polymer matrix are successfully demonstrated. The stacking approach of the composite sheets with a series connection suggests that the charging capability can be further enhanced depending on the number of stacking sheets. As an example, only double-layered sheets exhibit a ~5.7 V charging performance within ~150 seconds.