It actually gives out 5V or it says so on the label ?. In my experience they are often two barely related pieces of information. They often don't bother smoothing the output of chargers too well since the phone battery does that for them when they are used for their intended purpose. I had one that said 3.7V 500ma, it worked nicely at about 8.5 volts after I stuck a 470uF electroltyic in it to tame the ripple.