Generally, it is only possible to act on an original PoA (or notarized true copy of the original), and thus it is very important to keep the original(s) safe and secure where it can be easily located when needed, but not accessed inappropriately before.
There are three options:
Note that if there is a condition like “if I am incapable of managing my affairs” then someone will have to assess your capacity and make a determination of incapacity. This provides security against some over-zealous use of the POA, but, does impose costs and delay. As well, unless the POA document specifies either the method or person who will make the capacity determination, there may be uncertainty and doubt about who gets to make the determination.
You should revoke all prior PoAs when you make a new one. Revocation should be done expressly in the text of the new PoA. Only a person who is capable of granting a PoA is capable of revoking one. Accordingly, someone who has lost the capacity to grant a PoA cannot fire or terminate their attorney.
A PoA that is destroyed by the grantor is revoked. You can revoke a PoA by tearing it, burning it, or the like. Generally, if you make a new PoA you may wish to destroy previous ones. However, if there is any concern about the validity of a new PoA (for instance, if there is concern about the capacity of the grantor), then retaining a prior valid PoA can be helpful.
Normally, only an original PoA can be enforced. If the original has been lost, the presumption is that the testator destroyed it and thereby revoked it. This presumption can be overcome, but with considerable difficulty. It is very difficult to deal with a lost or misplaced PoA, and thus it is very important to keep original PoA in a safe location while also ensuring that they can be located when required.