Neither; usually they're fairly lousy regulation (if any).
Nobody cares since they only have to charge the
battery without burning it up (and the phone has
some smarts about that, inside).
But I have used many of them, with some added
filter caps and a 3-terminal regulator, to make low
cost (wall wart is free when the thing it powered,
died) power supplies for various uses (like testing
stuff at remote sites, when I don't want 50 pounds
of HP power supplies in the luggage and a 1-pound
wall wart lashup will do the job).