I don't have a Powacaddy, but have another brand, and I just got the Mid size Staff Bag, to put on mine.  It doesn't weigh much more and I liked the look of it better than the light weight staff bag or lightweight cart back (don't like the 14 club divider either).  So unless your Powacaddy has a smaller saddle for the bag to fit in you should be all set.  If you had a full size bag in it before, it should fit the same.  But I've found most all places will either allow you to bring your caddy in or take the bag out to you car and give it a try before making the final sale.  Good luck, they are great bags.