In case you forget the Plesk control panel's 'admin' password, then you have no other choice but to reset the password by logging into the remote server..
As the reset 'Administrator' password option [which in fact is for the admin user] is only available through logging into the Plesk control panel interface.
You can use the plesksrvclient.exe utility located in %plesk_bin% folder to either set up a new password or retrieve an existing one, follow these steps:

To obtain the current 'admin' password, execute this command in command prompt:
"%plesk_bin%\plesksrvclient" -get
To retrieve the password in command line you can also use the -nogui option [in case you are in CLI mode]:
"%plesk_bin%\plesksrvclient" -get -nogui > c:\plesk_passwd.txt
After that you can view the retrieved Plesk password in c:\plesk_passwd.txt file.

To set a new admin password execute the following command in command prompt:
"%plesk_bin%\plesksrvclient" -set <new_password> true
Hope that helps those, who find themselves in a fix after losing their Plesk's Admin login.... __Enjoy :smile: