Hello Edi,
I am sorry about the issue you experienced and I am happy to answer and assist you with this.
W3 Total Cache, depending on a configuration, needs to drop-in specific files in the wp-content in order for the caching to work.
Page Cache – advanced-cache.php
Object Cache – object-cache.php
Database Cache – db.php
If Database Cache is enabled W3TC detects if there is an existing db.php file and if so, there is a notification in the Wp-admin area that the db.php detected is not a W3 Total Cache drop-in and asks the user if the file should be removed. This means that W3 Total Cache does not automatically overwrites the dp.php file, it only removes that file and replaces it with its own if instructed to do so.
Every plugin that has the option for Database Cache needs to add its own db.php file in order to be able to perform as expected.
I hope you made a backup of your own db.php
Let me know if you have any other questions or suggestions.
Thanks!