I'm confused!
When someone is granted 'power of attorney', it enables them to manage the affairs of someone who is still living. They might not have even made a will. (If they have, the person with power of attorney has authority to handle the person's affairs in the way which best meets their needs. I can't envisage any circumstances where revealing the contents of that person's will, prior to their death, would be beneficial to the person who wrote the will. However, the person with power of attorney wouldn't be breaking any laws if he chose to reveal the contents of the will to anyone he chooses).
If a person, who wrote a will, has died, the executor of the will has to seek probate (which has nothing to do with 'power of attorney'). The executor is only obliged to to reveal the contents of the will so as to properly execute its requirements. (e.g. he must tell Fred that his granny left him �1000 but he doesn't have to tell Fred about the other provisions of the will).
However, once a will has been 'proved' and probate obtained, it becomes a public document and anyone can consult it.
Chris