@SteveHart 

There should be no issue to connect an extender of a different manufacturer to a different router. The extender or router may support or require specific settings depending on the models used. 

What model extender and router are you trying to connect and what issues are you having?

One key thing about extenders is they should be placed within a good WIFI signal area such as half way to the problem area. Some try to place it in the problem area and it does not work. Set up the extender at first about 5-10 feet from the router and after it is working, move it to the desired location.