Originally Posted by josh995
I believe it's actually the other way around. You can use a more powerful charger on a device that requires less, because the device will only draw the power it needs.
However don't use a charger that doesn't have enough power to charge the device, as the device could draw more power than the charger can provide and you risk catching the charger on fire.
This is how MacBook chargers work anyway. For example you can use an 85 watt charger to charge a 45 watt MacBook but you should not use a 45 watt charger to charge an 85 watt MacBook. (I have a few MacBooks that's why I used that reference).
Yep. A device will only pull the current that it needs, so high-powered PSUs on low-current devices is fine and dandy. The only difference in electrical output that would fry the phone would be voltage, but since all USB chargers "are supposed to" put out 5VDC, you're safe.
As for using chargers with less than sufficient current, I can only speak to my experience. Personally, I've never had an issue charging any of my more beefy devices (Nexus 7, Galaxy Nexus, or HTC One) off of an old 500ma charger that came with my Galaxy S (or a car charger with that same output, for that matter). The devices just charge slower. The PSU gets noticeably warm, but I'd never say it got hot to the point where the threat of combustion was even remotely possible. And as for the comparison to the MacBook charger, you're talking a difference of 40 watts, whereas these little USB chargers have a difference of maybe 2.5 watts (from the 500ma to 1A models). Not a lot of power there, really.
That said, if I were to buy a new one, I'd definitely get a charger that has the output spec to match or exceed the device's OEM charger.