The DC power supply in EX4300 switches is a hot-insertable and hot-removable field-replaceable unit (FRU): You can install it without powering off the switch or disrupting the switching function.
The Juniper Power Supply is a hot-insertable and hot-removable unit designed to power compatible QFX series switches. This internal, 650-watt plug-in module features ports to FRUs airflow.