Different Modules require different amount of power. Inline Power modules supplies the power to the IP phones. Cisco has inline power module to power the IP phones. You have to choose the correct power supply in order to support the various line cards, modules and Supervisor Engines on the switch. Cisco offers a tool called the Cisco Power calculator which can be used in order to choose the correct power supply for your switch. Launch the Cisco Power calculator and fill out the Product family, Supervisor Engine, Input voltage, line cards and the number of PoE devices. IP phones are the example for PoE devices and most of the IP phones belong to IEEE 802.3af Device - Class 2 (7W). Then the power calculator shows the results of different choices of Power Supplies. From that you can choose the required power supply. The power supplies successfully operate at their greatest capacity if the input voltage is between 200 and 240 volts AC.