A steam reheat process is provided to enhance a thermal power cycle, and particularly a renewable steam thermal cycle. An oxyfuel combustion gas generator is provided which combusts a hydrogen and/or carbon containing fuel with an oxidizer of primarily oxygen to generate products of combustion including steam and/or carbon dioxide. Water from the thermal cycle is directed to the reheater for mixing with the products of combustion within the reheater to generate a working fluid containing steam. This steam is routed through a turbine or other expander and power is outputted from the system. The water is optionally thereafter condensed and at least partially routed back to the thermal cycle. Any carbon dioxide within the working fluid can be separated in a condenser downstream of the expander for capture of the carbon dioxide, such that increased power output for the thermal power cycle is achieved without atmospheric emissions.