The AC power supply in EX4550 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. All the EX4550 switches that are powered by AC power supplies, except the EX4550-32F-S switches are shipped with one AC power supply pre-installed in the rear panel of the switches. EX4550-32F-S switches are not shipped with pre-installed power supplies; you must order them separately.