When using Parallels Plesk Panel Updater the following error occurs:
Error: Error: Unsupported config file
Not all packages were installed.
Please, contact product technical support.
The reason of the issue is in incorrect settings for Parallels Plesk Updater:
Home > Updates > Updater Settings > Parallels Plesk Panel Update source.
You should specify here "Source type: Parallels Plesk Panel Updates Server"
If you would like to keep another setting like this:
Source type: Network storage
then please specify actual "Source URL", also you should create local mirror for Plesk packages for the network storage available via "Source URL' as it is described in documentation here.