Can i sign back of paycheck payable to me if the check is in someone else's name but i have full power of attorney for them?

Generally speaking, it depends on what the power of attorney provides for as a person holding the power of attorney is a fiduciary to the person. Being a fiduciary means you must act in that person's best interest and for their benefit. It is difficult to answer your question without knowing more information. I would recommend consulting with an attorney that can review the power of attorney and know the full specifics of the situation.

I concur. It depends on the Fiduciary Power under the POA as to whether or not you have power to act in such a case. See .com under 'Find-A-Lawyer.

It depends on the powers granted in the POA. Typically you would sign your name stating it is under a POA granted by principal, and deposit the money into THEIR account, not yours. Remember you only have a right to use their money for their use. You should retain an attorney to review the POA to determine what rights are granted to you.