It depends on how the power is being supplied to the camera. When the camera is powered by the network cable connection it's nominal 48 volts. When powered by the external power connector it's 12 volts. 802.3af switches and injectors supply 48 volts. An 802.3af injector would likely want a 48 volt power supply. If you use a POE splitter or some other source to power the camera using its power connector, you'd want a 12 volt output from the splitter or other source. The only time you'd use a 12 volt supply with an injector is if it's a "passive" (not 802.3af) injector that's meant to have a passive splitter on the far end.