Unable to add apt-repository in Ubuntu-18.04

I access internet from the college proxy server. So, when I add an apt-repository as sudo add-apt-repository ppa:nilarimogard/webupd8, I get an error saying

Cannot add PPA: 'ppa:~nilarimogard/ubuntu/webupd8'.
ERROR: '~nilarimogard' user or team does not exist.

When I was on Ubuntu 16.04, I used to disable proxy settings and connect to mobile network and then add the repository.

When I do the same on Ubuntu 18.04, It shows 0% [Connecting to 172.16.2.30 (172.16.2.30)] [Connecting to 172.16.2.30 (172.16.2.30)] [Connecting to 172.16.2.30 (172.16.2.30)], where 172.16.2.30 is the proxy address. It is showing the above line even after disabling the proxy settings. How can I add the apt repository?

It is WebUpd8 team Atom PPA

sudo add-apt-repository ppa:webupd8team/atom
sudo apt-get update

Mind the ~ in your command.

Ehm, on 2nd reading: are you sure you copy/pasted this correctly?

You list 1 PPA and get an error on another PPA? If true, that seems fishy to me. If so the PPA is probably bugged. Might be an idea to report it on launchpad. Atom is NOT part of that PPA so it should NEVER tell you there is a problem related to the PPA belonging to Atom.

3rd: sudo add-apt-repository ppa:nilarimogard/webupd8 (Alin Andrei WebUpd8 PPA) works for me and does NOT show me an error.