I have installed Lubuntu 18.04 LTS on a Positivo Master N190I Notebook, but the wifi adapter didn’t work with this SO. Searching the solution I had to install a package from xenial to do the adapter work correctly.

First verify if you have a Realtek RTL8723AE using this command:

lspci | grep Wireless

Then add manually the PPA repository editing the file /etc/apt/source.list.

deb http://ppa.launchpad.net/hanipouspilot/rtlwifi/ubuntu xenial main 
# deb-src http://ppa.launchpad.net/hanipouspilot/rtlwifi/ubuntu xenial main

Now you have to install the packages below.

sudo apt update
sudo apt install rtlwifi-new-dkms linux-firmware

Reboot your computer and adapter will work correctly.