In power supply systems, continuity of service is a critical indicator of power quality. For certain critical loads, power interruptions can lead not only to economic losses but also to safety incidents or disruptions in public order. To ensure a stable power supply for such loads when the normal power source fails, Automatic Transfer Switching Equipment (ATSE) is widely used in low-voltage distribution systems. This article provides a systematic introduction to ATSE from four aspects: working principle, product classification, typical applications, and selection principles.