If you are creating a new windows application in C# then by default you dont get any app config file. To answer your question, Yes C# does support appconfig files. You can add them as shown below :
Then you can exploit its XML to set some values as shown in the example below.
<configuration>
<appSettings>
<add key="TestFlag" value="false" />
<add key="TestUser" value="somevalue" />
<add key="TestPass" value="somevalue" />
<add key="TestRole" value="SA" />
<add key="TestModeOfOp" value="dssaas" />
<add key="TestFetchRef" value="" />
<add key="TestFetchQuoteNo" value="" />
<add key="TestVersionNo" value=""/>
<add key="TestProdCode" value="233" />
<add key="TestSessionID" value="123123"/>
<add key="TestServiceIP" value="192.168.30.21"/>
</appSettings>
</configuration>
In my case I use APP.XAML to get the value from the app.config in its application_startup.