Home is currently on 50/20 Plan and running an old Telstra modem.
Have got a AC68U that I keep in another house as spare.
have been wanting to upgrade from 50/20 to 100/20 but afraid I have to pay for a new modem instead of using the one I have.
Can the 100/20 plan work on the ASUS DSL-AC68U?
Assuming you're on a FTTN/B plan and going up a speed tier, should work with either device.
I had a AC68U which had no issues handling 100/20.