GetPleskPassword(); Tested for Plesk 8.6

gistfile1.cs

        public string GetPanelPassword()
        {
            var plesksrvclient_exe = Path.Combine(Environment.GetEnvironmentVariable("plesk_bin", EnvironmentVariableTarget.Machine),"plesksrvclient.exe");
            CoreHelper.Exec(plesksrvclient_exe, "-get  -nogui");

            return System.Windows.Forms.Clipboard.GetText();
        }