You don't need an additional adaptor as your NBN modem/router will be connected directly to your wall socket given that the technology is under NBN FTTN (Fibre to the Node).
Once the NBN is installed and activated, the ADSL service will be disconnected.
You may refer to the setup here: NBN Fibre to the Curb (FTTC) Setup Guide.
You don't need an adapter, but an NBN NCD box. If it's still not installed in the premises, then an NBN technician visit is required to install it.