I had the following solution:
change my.ini in a [mysqld]
section like this:
#default_authentication_plugin=caching_sha2_password (comment line!)
default_authentication_plugin=mysql_native_password (new line)
Connect to your MySQL under root in a command line client
and execute:
ALTER USER 'root'@'localhost' IDENTIFIED WITH mysql_native_password BY 'xxx';
Where xxx
is your current password.