I have problems with Internet connection with most Ubuntu DEs, except KDE – network managers don't allow me to establish a DSL PPPoE connection.
So I'm thinking to buy a router – conventional, I don't want a WiFi router, to take the task of performing the PPPoE connection away from the desktop.
My Internet cable which goes into my apartment has RJ-45 connector, which I plug in right into Ethernet port of my PC, no other devices being used.
I used to do it by creating DSL connection with 'pppoe' in the service field, typing password and login. Also I could use pppoeconf command for that isn't available anymore for last *buntu releases.
Such issue with DSL ppoeconf is in:
*buntu (GNOME3,XFCE,Ubuntu Mate) (except KDE) 16.04/18.04/18.04.1/18.04.2/18.04.3, though it works from live-usb.