Question about Devolo dLAN 550+ WiFi extension

Probably not, if I understand you correctly this does not work.

Here's how Powerline adapters work:
1. Powerline adapters communicate with each other through power lines which are installed in the house. Usually, Powerline Adapters can only communicate with each other as long as they are used in the same house or apartment.

2. You need one Powerline adapter which is connected to your modem / router to "bring Internet into the power lines"
3. Further Powerline Adapters can then connect to the first one (through the power lines), which is connected to your modem / router and the Internet can be accessed from any device which is connected to that second (or third, fourth, etc.) power line adapter.
The Devolo 550+ Wifi creates a WiFi-Network which allows you to connect to the Internet with any Smartphone / Laptop / ..., as long as there is another power line adapter in the same house / apartment which is connected to a modem / router.

From what you're telling us (your son living in a home with no Internet), this adapter will not work. You might want to have a look at "mobile wifi Routers": You can put a SIM-Card (with a data plan) into these and they create a wifi-Network which can then be used to access the Internet with every WiFi-enabled device. For this solution, you need:
a) Acceptable Signal strength of the mobile phone Network
b) a SIM-Card with a data plan.
Mobile Routers: https://www.digitec.ch/en...