CG, durable POA is just that, it allows for you to be an agent now and also when he/she is incapacitated. There is a little used (state-dependent) General POA that is only for incapacity, and also what's sometimes called "springing POA" for the same purpose. Those aren't really a factor but do exist. Most states consider all POAs to be durable, unless otherwise specified.
For example, my DH and I have durable POA paperwork (the generic ones drawn by our attorney), that we don't need to use but have, just in case.
I also have Schwab-specific POA for all of his accounts held there, which I do use to make trades and whatnot.
Also please note that all POA granted powers expire at death.
“One day your life will flash before your eyes. Make sure it's worth watching.”
Gerard Arthur Way