If a principal designates another as the principal's agent by a written power of attorney which contains the words "This power of attorney shall not be affected by disability of the principal," or "This power of attorney shall become effective upon the disability of the principal," or similar words showing the intent of the principal that the authority conferred is exercisable notwithstanding the principal's disability, the authority of the power of attorney is exercisable by the agent as provided in the power of attorney on behalf of the principal notwithstanding any later disability or incapacity of the principal or later uncertainty as to whether or not the principal is dead or alive.
SDCL 59-12-3