If you have multiple users on one Plesk account and need to FTP content without editing the FTP password, you can retrieve the password from MySQL.
To Retrieve a Plesk Password From MySQL
mysql -uadmin -p`cat /etc/psa/.psa.shadow`, and then press Enter. use psa;, and then press Enter. select * from sys_users;, and then press Enter. select * from accounts where id = 2;, and then press Enter.