Well, let's be precise about terminology. Just for people who come along later – I realize you probably know these things already.
"OneGet" isn't a thing per se; it's "PowerShell Package Manager.""OneGet" was a very early pre-release name.
And the PPM uses _providers_ to connect to repositories. The idea is that PPM can talk to any repository – NuGet, file shares, etc – if you have the right provider. Register-PackageSource has a -ProviderName parameter, which is where you tell it which provider to use. That's a mandatory parameter.
Different providers accept different sources. For example, the Chocolatey provider is usually used with a URL (ideally HTTPS so that you can mutually authenticate the server).