With the large-scale integration of renewable energy sources, conventional hydro and thermal generators have become scarce resources for maintaining transient frequency and voltage stability. The participation of non-synchronous components in transient power angle stability control has emerged as an inevitable trend. However, existing research predominantly focuses on synchronous generators, and insufficient attention has been given to quantifying the impact of non-synchronous components on transient power angle stability. This research gap substantially hinders the effective optimization of decision-making involving non-synchronous components. The novel concept of Transient Energy Equilibrium Point (TEEP) in power systems is introduced in this paper, and the calculation method for TEEP is presented using a two-machine three-node five-branch model. The dynamic characteristics of TEEP and its distinctions from the oscillation center are analyzed. Furthermore, building upon TEEP's intrinsic energy self-regulation properties and the fundamental principle of transient energy conservation, a quantitative transient power angle stability impact degree index for non-synchronous components is proposed, derived from cumulative energy deviation. This index furnishes a quantitative basis for optimization of decision-making involving non-synchronous components. Simulation results, obtained through the two-machine electromagnetic transient (EMT) simulation system, validate TEEP's variation characteristics and the effectiveness of the transient power angle stability impact degree index.