Let me just amend the author's statement about SSI transactions. I was informed by both the Social Security Administration, as well as the Office of Personnel Management and the VA, individually, that they do not recognize POAs for financial/asset matters. Instead, the person handling finances must go to the SSA office and fill out a "Responsible Party" form. (In their convoluted logic, they believe that anyone can get a signature, witnesses and notary for a POA to defraud the recipient. Note that the recipient does not have to be there to affirm the Responsible Party designation; the SSA sends a letter a couple of weeks later to the recipient confirming that John Doe just signed the forms, is that okay?. Go Figure...if you control their mail as well they never get the confirm.)
In any event, the Responsible Party must maintain a log of all expenses paid for the recipient out of their SSI benefit (or pension if in re: a govenrment employee) and submit annually. The assumption of funds use in general is food, medical, living expenses first, savings (that's a laugh) with whatever is left over. Have no idea what the level of enforcement is, but I'm sure there is some bean counter/auditor sampling these.
So botton line is you need the POA, but for government related SSI, annuities etc., you need the Responsible Party designation.