A savings bank may continue to recognize the authority of an individual holding a power of attorney in writing to manage or to make withdrawals, either in whole or in part, from the deposit account of a customer or member until it receives written or actual notice of death, or of adjudication of incompetency of such member, or revocation of the authority of such individual holding such power of attorney. Payment by the savings bank to an individual holding a power of attorney prior to receipt of such notice shall be a total discharge of the savings bank's obligation as to the amount so paid.