There are 3 ways to power up a device:
The external power supply unit
Power over Ethernet (PoE) from a switch
A Midspan power injector/inline power patch panel (a device that sits between a switch and an IP Phone)
Both the Cisco proprietary and IEEE 802.3af provide power to connected devices over switch port pins 1,2,3,6. When using midspan power injectors/inine power patch panels, power is sent to the connected device using pins 4,5,6,7
Reminder : For the Cisco proprietary method, the switch sees a coming back FLP and for 802.3af, the switch see a resistance of 25K ohms on a voltage applied (-2,8 to -10V)