ODP Connect String with Oracle Wallet
This works for me:

"User Id=/;Data Source=DBNAME"


Please note that many people (including myself) are having issues getting an Oracle Wallet to work with the 12c managed driver.  You may need to enable SSL client authentication.  See the following thread on the Oracle Community site for details.

https://community.oracle.com/thread/2590420

As an aside, I'd recommend not overriding the app.config for powershell.exe, and instead using the machine.config.  If you don't see the entries in there to edit, run the configure.bat script found in ORACLE_HOME\odp.net\managed\(x64|x86)\

ise ([System.Configuration.ConfigurationManager]::OpenMachineConfiguration().FilePath)


And then in your Powershell script, you can also load the driver without having to know the path to the DLL:

[void][reflection.assembly]::Load("Oracle.ManagedDataAccess, Version=4.121.2.0, Culture=neutral, PublicKeyToken=89b483f429c47342")