Configure proxy settings in Notepad++ via Plugin Manager

From the command line we have to access to the \updater folder of Notepad ++

> cd /d C:\Program Files (x86)\Notepad++\updater

then :

> gup -options

The window for proxy configuration is displayed:

Open cmd and type:

cd /d C:\Program Files (x86)\Notepad++\updater
gup -options

A dialog comes up to set the proxy settings.

with version 7.6.6 (april 2019) (probably onwards), you can run notepad++ as admin, use menu '?' > Set Updater Proxy... close notepad++ and open it again as standard user.