<p>Under grid faults, the grid-forming (GFM) converters may experience transient synchronization instability. With the prevalence of GFM converters, the transient stabilization of parallel GFM converters has become an urgent issue. To fill this gap, this article conducts an in-depth analysis of the transient stability of two-machine grid-connected systems when power synchronization control (PSC) is implemented by the converters. A transient mathematical model is developed to provide insight into the overdamping characteristics of PSC-based multi-machine systems in arbitrary power angle direction. Thus, it is pointed out that the existence of the stable equilibrium point is a sufficient and necessity condition for maintaining transient stabilization. By introducing power curved surfaces and contour lines, the power balance relationship of the system and the effect of the active power reference of the converters on transient stability are analyzed from three-dimensional and two-dimensional perspectives. Finally, time-domain simulations considering grid faults are performed to validates the theoretical analysis.</p>