Thanks a lot, LaoMao. I found the answers in the link you provid

A power of attorney may be special or limited to one specified act or type of act, or it may be general, and whatever it defines as its scope is what a court will enforce as being its scope.

They will usually keep an original copy for their records.

So it means that I need many copies of general power of attorney, while my wife is out of the country.

Thanks