Abstract: In computational electromagnetics, the discontinuous Galerkin (DG) method has been widely adopted as an effective approach for handling non-conformal meshes, demonstrating remarkable flexibility in addressing challenges posed by complex geometries. While traditional interior penalty discontinuous Galerkin (IEDG) methods impose stringent requirements on non-conformal meshes due to the necessity of computing stabilization terms, a simplified DG formulation (SDG) has recently emerged that eliminates stabilization terms while maintaining comparable accuracy in non-conformal mesh computations. This paper first elucidates the fundamental principles of the SDG method. Subsequently, it systematically categorizes various non-conformal mesh types encountered in practical partitioning scenarios through explicit definitions and illustrative examples. Furthermore, the study investigates the relationship between different defective non-conformal mesh configurations and SDG performance, quantitatively evaluates their impacts on computational results, and provides comprehensive discussions on SDG's behavior under diverse mesh conditions.