I have no idea what extension wire you are talking about.    I looked up  the Hamuti chicken door.   It seems to be powered by a solar power source.  If you are asking what kind of wire to be used to connect the two????     Any type of light wire would work.   There is not much current in regards to quantity  (amps) in such a setup.   
If there are certain type of end connectors,,,, then get what the door manufacturer  suggests. 
BTW,   Renoldy  may be a spelling error.    I did find RENOGY,,,,,, a company that specializes  in solar panels  to power your home.  (when living off grid)
WISHING YOU BEST,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,and 
