Problems with RelocateFile property in the Restore-SqlDatabase cmdlet

You can do this in a version-independent way:

$sqlServerSnapinVersion = (Get-Command Restore-SqlDatabase).ImplementingType.Assembly.GetName().Version.ToString()
$assemblySqlServerSmoExtendedFullName = "Microsoft.SqlServer.SmoExtended, Version=$sqlServerSnapinVersion, Culture=neutral, PublicKeyToken=89845dcd8080cc91"

$RelocateData = New-Object "Microsoft.SqlServer.Management.Smo.RelocateFile, $assemblySqlServerSmoExtendedFullName"('MyDB_Data', 'c:\data\MySQLServerMyDB.mdf')
$RelocateLog = New-Object "Microsoft.SqlServer.Management.Smo.RelocateFile, $assemblySqlServerSmoExtendedFullName"('MyDB_Log', 'c:\data\MySQLServerMyDB.ldf')
$myarr=@($RelocateData,$RelocateLog)
Restore-SqlDatabase -ServerInstance DEV\DEMO -Database "test" -BackupFile $backupfile -RelocateFile $myarr

This looks like a difference in the version of SMO that you have loaded and the one that Restore-SqlDatabase expects. There are probably two approaches here...

1. Make sure that the versions match.
2. Use the Microsoft.SqlServer.Management.Smo.Restore.SqlRestore method instead of the Restore-SqlDatabase cmdlet.

I have extracted the relevant pieces from a larger script below. It is untested in this form and there are a few variables such as $ServerName which are assumed to be available but it should be enough to get you going.

    if($useSqlServerAuthentication)
    {
        $passwordSecureString = ConvertTo-SecureString -String $password -AsPlainText -Force;

        $serverConnection = new-object Microsoft.SqlServer.Management.Common.ServerConnection $ServerName, $UserName, $passwordSecureString;

        $server = new-object Microsoft.SqlServer.Management.Smo.Server $serverConnection;
    }
    else
    {
        $server = new-object Microsoft.SqlServer.Management.Smo.Server $ServerName;
    }

    $dataFolder = $server.Settings.DefaultFile;
    $logFolder = $server.Settings.DefaultLog;

    if ($dataFolder.Length -eq 0)
    {
        $dataFolder = $server.Information.MasterDBPath;
    }

    if ($logFolder.Length -eq 0) 
    {
        $logFolder = $server.Information.MasterDBLogPath;
    }

    $backupDeviceItem = new-object Microsoft.SqlServer.Management.Smo.BackupDeviceItem $Path, 'File';

    $restore = new-object 'Microsoft.SqlServer.Management.Smo.Restore';
    $restore.Database = $DatabaseName;
    $restore.Devices.Add($backupDeviceItem);

    $dataFileNumber = 0;

    foreach ($file in $restore.ReadFileList($server)) 
    {
        $relocateFile = new-object 'Microsoft.SqlServer.Management.Smo.RelocateFile';
        $relocateFile.LogicalFileName = $file.LogicalName;

        if ($file.Type -eq 'D'){
            if($dataFileNumber -ge 1)
            {
                $suffix = "_$dataFileNumber";
            }
            else
            {
                $suffix = $null;
            }

            $relocateFile.PhysicalFileName = "$dataFolder\$DatabaseName$suffix.mdf";

            $dataFileNumber ++;
        }
        else 
        {
            $relocateFile.PhysicalFileName = "$logFolder\$DatabaseName.ldf";
        }

        $restore.RelocateFiles.Add($relocateFile) | out-null;
    }    

    $restore.SqlRestore($server);

For solution #1, you need to specify assembly qualified name when you instanciate relocate file to use correct assembly.

$RelocateData = New-Object 'Microsoft.SqlServer.Management.Smo.RelocateFile, Microsoft.SqlServer.SmoExtended, Version=11.0.0.0, Culture=neutral, PublicKeyToken=89845dcd8080cc91' -ArgumentList "MyDB_Data", "c:\data\MySQLServerMyDB.mdf"
$RelocateLog = New-Object 'Microsoft.SqlServer.Management.Smo.RelocateFile, Microsoft.SqlServer.SmoExtended, Version=11.0.0.0, Culture=neutral, PublicKeyToken=89845dcd8080cc91' -ArgumentList "MyDB_Log", "c:\data\MySQLServerMyDB.ldf"
$file = New-Object Microsoft.SqlServer.Management.Smo.RelocateFile($RelocateData,$RelocateLog) 
$myarr=@($RelocateData,$RelocateLog)
Restore-SqlDatabase -ServerInstance DEV\DEMO -Database "test" -BackupFile $backupfile -RelocateFile $myarr

Hope it helps !

Used @Linhares solution except the Snapin assembly's version of 15.0.0.0 did not match the referenced Microsoft.SqlServer.SmoExtended version 15.100.0.0.

So tweaked this line to get the version directly from the referenced assembly.

$sqlServerSnapinVersion = ((Get-Command Restore-SqlDatabase).ImplementingType.Assembly.GetReferencedAssemblies() | ? { $_.Name -eq "Microsoft.SqlServer.SmoExtended" }).Version.ToString()