Capacity markets (CMs) have been widely analysed and implemented in various regions to enhance the capacity adequacy and supply security in power systems with high renewable penetration. This study compares the performance of two market designs

an energy market combined with a CM and an energy-only market

using a capacity expansion model that incorporates long-term energy storage (ES). This study contributes significantly to the debate on CM by quantifying the improvement in the system reliability. Through simulations conducted on provincial power systems in China

we demonstrate that introducing a CM significantly enhances the system reliability by providing a stable revenue stream that incentivises capacity investments. Additionally

the effectiveness of implementing a CM is analysed through simulations under various market conditions

thereby presenting various advantages. Furthermore

the results of this study indicate that the reliable availability of conventional technologies is essential for future power systems with high renewable energy penetration. The supply security cannot be ensured with an excessive penetration level of renewable energy sources

despite long-term ES. These findings present critical insights into the design of hybrid electricity markets for transitioning power systems.