I believe Princess uses the same company for all of their rentals but I'm not sure.
Princess tends to hire their own staffs to do many things that other cruise companies contract out, including shipboard shops. Thus, I would not be surprised if Princess set up their own formalwear rental operation, although I have no firm knowledge one way or the other.
My husband used the cruise lines recommended formal wear provider and it worked out great. We used it last fall and it was in our cabin when walked in. It fit perfectly. He did go to Nordstrom and have a complimentary fitting prior to booking the reservation. I highly recommend you do the same to get the proper fit and not guess that sort of thing. You will be more compfortable.
I just ordered my formal wear for our cruise on the Star Princess leaving on March 23rd. Cruiseline Formalwear is the company that Princess uses and I had no problems with them during my Alaska cruise in July 99. Their webpage is: