Yep, essentially a "passive" (NOT 802.3af/at/bt) injector has provisions to:
- allow data (only) to pass through the device
- inject the voltage from the DC jack to the "PoE" side
Most if not all such devices are bi-directional. i.e. the splitter has provisions for:
- allow data (only) to pass through the device
- split voltage from "the PoE" side and provide it to the DC socket (or - in other words - inject the voltage from the "PoE" side to the DC socket)
The pairs of passive splitters that are common for non-PoE cameras are actually two of the same device splitter/injector the difference between them is only that one has a DC jack and one a DC socket.
This doesn't mean that all injectors can also be used as splitters (with the addition of a DC jack/socket "gender changer"), but most will, and the Mikrotik ones can, see as reference:
MikroTik RBGPOE - usable as PoE splitter?
BUT with the limitation of not being detected as a "high voltage" device, so to use 48 V you need to set PoE to forced on:
RB5009Upr PoE out to RB5009Upr - Voltage too high using RBGPOE