(a) The appointment by a court of a guardian or other fiduciary charged with the management of the principal's property or the care of the principal's person shall terminate all personal powers of attorney.
(b) After the appointment of a guardian or other fiduciary charged with the management of the principal's property or the care of the principal's person, the agent is accountable to such guardian or other fiduciary as well as to the principal as to any personal powers of attorney which the agent continues to hold. A guardian or other fiduciary shall only have such powers to revoke or amend the powers of the agent as shall be given to such guardian or other fiduciary by the court.