Damage to the adapter has become an obstacle to the life of the luminaire today. The user cannot judge whether the LED downlight that is not lit is damaged by the downlight itself or the adapter is damaged, so that the downlight is directly replaced with the adapter, resulting in waste of resources. The plug-in adapter successfully solves this problem. When the downlight is not lit, the user can directly check the indicator light on the downlight to determine whether the adapter is faulty. The adapter is reinforced with insulation to ensure that no body is in direct contact with any live parts, and the adapter can be replaced in the event of an uninterrupted power supply. Let the LED light source truly play its due life, safe and convenient, and also complete the significance of energy saving and environmental protection.