postgresql does not appear in Data Source when generating .ADO.net Entity Data Model
I was confused while 3 days becuase the same problem.
But, I found solve this problem:
install .vsix file in your visual studio environment. https://github.com/npgsql/npgsql/releases/tag/v3.1.8 (NpgsqlDdexProvider)
install Npgsql and EntityFramework6.Npgsql by Nuget Package Manager.
Build your project. (For apply configuration of modified App.xaml by Nuget)
You can use ADO.NET Entity Model Generation.
Also, dotConnect not support Entity Model in Express version. It supported in only commercial version.
But currently, Npgsql has immediately close bug in EDM. so, I finding solution.
I had been the same issue for a while. Then, I've tried to install dotconnect https://www.nuget.org/packages/dotConnect.Express.for.PostgreSQL/7.4.506/. And, it works! hope this help.
This issue can been solved by adding a Visual Studio extension provided here: http://www.npgsql.org/doc/ddex.html