обо всём понемногу...
How to install

Download extension and copy to SQL_DEVELOPER_HOME/sqldeveloper/extensions/ and run SQL Developer.

Note for Mac OS Version: copy extension to SQLDeveloper.app/Contents/Resources/sqldeveloper/sqldeveloper


In the menu “File” you will see new menu item “Show Me Database Password


If you click on menu item “Show Me Database Password”, then displays a window that contains one table with three columns: connection name, user name and decrypted password: