I have some folders I created for Power Users. I only want the specific user and Administrator to have access to these folders. Problem is, when I explicitly disallow the user group "Users", Administrator no longer has access to the folder. Administrator is not part of the group "Users".
I don't want to have to explicitly deny access to each user in the "User" group, "Power users" can add these accounts which would be a security breach. Besides that, it's a PITA.

Is this a domain or a stand alone PC?

Quoted: I have some folders I created for Power Users. I only want the specific user and Administrator to have access to these folders. Problem is, when I explicitly disallow the user group "Users", Administrator no longer has access to the folder. Administrator is not part of the group "Users". I don't want to have to explicitly deny access to each user in the "User" group, "Power users" can add these accounts which would be a security breach. Besides that, it's a PITA.

Everyone that logs on to that machine is a member of the "User" group. If you explicitly deny access to that group, you've effectively locked out everyone but the owner of the file/folder. Don't explicitly deny access to the User group, just remove all permission to it completely. Then add the Power Users group and give them the appropriate permissions.