Load frequency control (LFC) is widely employed to keep smart grids stable and secure. This paper proposes an adaptive resilient LFC scheme for sub-systems of smart grids under denial-of-service (DoS) attacks with energy constraint. Firstly, a resilient triggering communication scheme is introduced, where the triggering condition includes the uncertainty item induced by DoS attacks. Secondly, an adaptive resilient event-triggering LFC scheme is proposed to further reduce the communication burden and defeat the DoS attacks, where the event-triggering parameter can be dynamically adjusted. Third, a stability criterion is derived for Proportional Integral-based LFC systems by employing Lyapunov theory. Finally, to validate the proposed control scheme, case studies are carried out based on three different LFC power generation systems including one-area, two-area and three-area models. The simulation results clearly demonstrate that the proposed adaptive resilient LFC scheme can reduce the communication burden while defeating DoS attacks by comparing with resilient event-triggering LFC scheme and event-triggering LFC scheme in term of defense effect and average triggering period.