Csharp/C Sharp by API/System.Security.Principal/WindowsBuiltInRole

WindowsBuiltInRole.PowerUser

using System;
using System.Security.Principal;
class MainClass
{
  public static void Main() 
  {
    WindowsIdentity wi = WindowsIdentity.GetCurrent();
    WindowsPrincipal prin = new WindowsPrincipal(wi);
    if (prin.IsInRole(WindowsBuiltInRole.PowerUser)) 
    {
      Console.WriteLine("You are a member of the Power User group");
    }
    else
    {
      Console.WriteLine("You are not a member of the Power User group");
    }
  }
}