I have checked the uptime history on the status page (see here for yourself http://status.telerik.com/) and am unable to poinpoint any downtime for the server in the past 90 days. I am able to connect myself with a quick check via Visual Studio.
Using the URL itself will not list the packages, the expected result is this:
<service xmlns:atom="http://www.w3.org/2005/Atom" xmlns:app="http://www.w3.org/2007/app" xmlns="http://www.w3.org/2007/app" xml:base="https://nuget.telerik.com/nuget/">
On your dev machine, double check that you're using HTTPS and there is no proxy. I have seen issues with Visual Studio for Mac in this regard before. In these cases, the fix was to just delete the Package source and re-add it.
If you're on windows, also delete the cached credential in the Windows Credentials manager. If you're not familiar with the Crednetial Manager, see the steps here https://docs.telerik.com/devtools/xamarin/installation-and-deployment/telerik-nuget-server?#troubleshooting
Lance | Team Lead - US DevTools Support
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