I am using Power BI desktop Auguest 2019, PostgreSQL x64 ODBC driver 11.03.00.00 (tried both Unicode and ANSI), and seems like passwords are not transimitted to Postgres server when special some characters are included. For example, password Ab!@#$%^&*()-_=+ becomes Ab!@#$�*()-_=+ when it reaches PostgreSQL server.
I tested ODBC administrator, and I saw password are transmitted correctly from ODBC client to Postgres server.
The screenshot shows when password is passed correctly to Postgres server, from ODBC administrator:
And the screenshot below shows password is not passed correctly to Postgres Server from Power BI desktop: