If the charger output current (the A or mA part) is at least as much as the original charger of the 9, there won't be a problem - the phone will only draw as much as it's designed to draw. If the number is less it'll work, but it'll take longer to charge. (Your 100 Watt light bulb - which draws about 1 Amp - is connected to a "charger" - the power coming into your house - with at least 200 Amps, but it still only draws 1 Amp. Connect it to a 1/2 Amp supply and it'll glow a kind of dull red, because it's not getting enough current. But it won't draw too much current from a larger supply source.)
I regularly charge phones from a 5 volt, 100 Amp supply (or a few others that supply somewhat less current) with no problem. As long as the 5 Volts (or 5.2 Volts - it won't make a difference) is there, it's fine. If you try charging a phone from a charger that has a 12 Volt output, you'll have a problem.