Re: Backup plugin?
I think that predominately most will be backing up by performing SQL dumps of the DB. it’s the usual and safest method and simple to do via a tool such as MyPHPAdmin.
I think you’ve said that you have a Plesk control panel available to you? Plesk panels should have access to the DB server via MyPHPAdmin which will allow you to select the appropriate DB and download a full dump of all tables.
The codex.wordpress.org has guides on how to perform SQL backups.