Adding PostgreSQL on Oracle SQL Developer

1. Download the JDBC driver from  https://jdbc.postgresql.org/download.html#current.
2. Wget https://jdbc.postgresql.org/download/postgresql-42.2.14.jar
3. Copy the jar file into C:\Program Files\sqldeveloper\jdbc\lib 
4. Launch Oracle SQL Developer
5. Click Tools -> Preferences > Database > Third Party JDBC Driver > "Add Entry..." >  Go to "C:\Program Files\sqldeveloper\jdbc\lib" and select "postgresql-42.2.14.jar " > OK.
6. That's it.