Why internal and external power supply options?

All 24- and 48-port models of Cisco Business switches come with internal power supply because these devices are normally rack mounted and connect directly to AC power outlets. Eight- and 16-port models come with both internal and external power supply options. The external power supply models have smaller enclosure sizes so they can better fit into small spaces like on the desk, in the meeting room, or in the classroom. The internal power supply models have slightly larger enclosure size but provide the benefit of easier connection to AC power outlets.

All internal and external power supplies come with the switch so there is no need to purchase the power supply separately.