If a power of attorney has been signed...and a new one after surfaces is that the one that is valid?

If a power of attorney has been signed, but then the signer designates a new power of attorney after that is that a valid doent? or do you have to remove the original in some way? on accident a relative signed the first doent. So If a power of attorney was signed and the signer changes their mind and signs a new one and it is all notarized etc. Is that the one that takes over?