Depends what country u from they probably call it by different names. You can buy any generic one as long as SAME VOLTAGE, AMPerage equal or better, and the plug (they all look the same but they are not) must be of the same size. Those are coaxial power plug with a OD (Outer Diameter) and ID (Inner Diameter) measurements, and typically Negative on the outside of the plug and positive inside, but check to be sure.
If all these too much, just order one from the router's vendor.