All access to non-Infragistics PowerShell Nuget access fails without Infragistics Credentials
Once I set Visual Studio 2017 to use Infragistics licensed feed all PowerShell command line references to NuGet warn and then fail.
Registered Sources:
PS C:\WINDOWS\system32> Get-PackageSource
Name                         ProviderName     IsTrusted  Location
----                             ------------               ---------      --------
nuget.org                   NuGet                  False         api.nuget.org/.../index.json
Infragistics Feed        NuGet                  False         packages.infragistics.com/.../licensed
PSGallery                  PowerShellGet    False         www.powershellgallery.com/.../

Example Command which Fails:

PS C:\WINDOWS\system32> Install-Package Microsoft.EntityFrameworkCore.Tools
WARNING: Cannot access 'packages.infragistics.com/.../licensed'. Are you missing 'Credential' parameter in the cmdlet?