private string PowerShellExecutor(string script) {
    string outString = "";
    var shell = PowerShell.Create();
    shell.Commands.AddScript(script);
    var results = shell.Invoke();
    if (results.Count>0)
    {
        var builder = new StringBuilder();
        foreach (var psObj in results)
        {
            builder.Append(psObj.BaseObject.ToString() + "rn");

        }
        outString = Server.HtmlEncode(builder.ToString());
    }
    return outString;
}

<div class="col-md-12">
            @Html.DropDownList("ddlDirectory", new SelectList(PowerShellExecutor(AppDomain.CurrentDomain.BaseDirectory + "Shell\Get\ADDomain.ps1")), "Select Domain", new { @class = "form-control"})
</div>