This paper employs numerical simulation methods to first investigate the mixing characteristics of a supersonic mixing layer with a convective mach number of 0.32 under the influence of both conventional plasma synthetic jet actuators and ram-typed plasma synthetic jet actuators. Subsequently, the study explores the impact of the compressibility of the supersonic mixing layer on the mixing enhancement achieved by the ram-typed plasma synthetic jet. The mixing performance of the plasma synthetic jet was evaluated using the velocity thickness, vorticity thickness, gain factor, and Reynolds stress of the mixing layer. The results indicate that both actuators can effectively perturb the supersonic mixing layer. The vortex-wave effect induced by the plasma synthetic jet triggers early transition of the K-H vortices in the mixing layer, forming large-scale vortex structures. This enhances momentum transport characteristics, thereby effectively promoting the mixing of the upper and lower streams. The ram-typed plasma synthetic jet actuator, benefiting from the intake flow and aerodynamic ramp effect at its inlet, demonstrates superior mixing performance compared to the conventional plasma synthetic jet. The ram-typed plasma synthetic jet exhibits excellent mixing performance across supersonic mixing layers with varying compressibility levels. Moreover, the sensitivity of the supersonic mixing layer to jet disturbances increases with higher compressibility.