On server with Parallels Plesk Panel versions 8.x, 9.x and above admin password is stored in file /etc/psa/.psa.shadow.
To get root password simply run following command:
Since version 10 admin password stored in file /etc/psa/.psa.shadow is encrypted. Use the following command to get admin password in plain text:
Despite version of Parallels Plesk Panel you may use the following command to login to mysql with root privileges:
mysql -uadmin -p`cat /etc/psa/.psa.shadow`