Answer
To determine database provider it is necessary to run regedit.exe and go tofor x86
HKEY_LOCAL_MACHINE\SOFTWARE\PLESK\PSA Config\Config
for x64
HKEY_LOCAL_MACHINE\SOFTWARE\wow6432node\PLESK\PSA Config\Config
The value of key "PLESK_DATABASE_PROVIDER_NAME" is the database provider which Plesk uses for database storage.
The database providers that could be listed here are:
- Jet
- MySQL
- MSSQL
Source: http://kb.parallels.com/en/3453