Plug the TPL-420E directly into an outlet.  Avoid connecting them to extension cables, power strips or surge protectors.  The TPL-420E has built-in surge protection    Reset the units and ensure they are configured with the same Network ID or use the sync button to connect them.  
It is not recommended to use this product on electrical systems that use AFCI circuit breakers or plugged into GFI protected outlets as this may cause performance degradation or loss in connectivity.