How can we make Controlling PMO efficient in large organizations?

A controlling PMO will take some authority from the project manager, or at least it will feel that way. But look at the bright side, they can also share some of the responsibility.

What is difference between controlling PMO, PM and Delivery manager? As mentioned by Rami, controlling PMO can involve in Resource management across projects and programs but for that he needs to understand scope boundaries of project so resource requirement raised by PM's are genuine. So delivery manager as to ensure the resource requirements raised by PM across projects are valid for the project pools under him. So please correct if controlling PMO plays part role of Delivery manager, PM etc.. I have been currently given role & responsibility of PM, controlling PMO,Delivery Manager etc since there was no Delivery manager in place.