In this letter, we propose a novel dynamic power allocation scheme for hybrid non-orthogonal multiple access (DH-NOMA). The exact expressions for the outage probabilities and their asymptotic approximations at high signal-to-noise ratio are derived in DH-NOMA systems. Both Monte Carlo simulations and analytical results are used to compare the proposed scheme with the existing works, such as NOMA based on fixed power allocation (F-NOMA) and cognitive radio inspired NOMA (CR-NOMA). The provided results demonstrate that the DH-NOMA scheme can always achieve better outage performance than the traditional orthogonal multiple access, and achieve a more balanced tradeoff between the two user individual rates than F-NOMA and CR-NOMA.