Rules of thumb:
Too many amps will fry living things, not electronics. If you plug in a 2A charger on a device that was "designed" for a 1A charger, nothing unusual will happen (though it may charge faster). If you send even 100mA (that's 5% of the current provided by the stock charger) through yourself, you risk death, particularly if the circuit crosses your heart. That said, the 5V that USB provides isn't likely to be able to break through the resistance of your skin, provided it's dry, so you don't need to be too fearful of exposed USB wires, even from a 2A charger.
Too many volts will fry electronics, though not necessarily living things. The static shock you get in the winter when you touch a doorknob is in the thousands, if not millions of volts, but obviously isn't harmful to you. This is because there's not much current flow. That same spark is potentially deadly to electronics. However, sustained high voltage can break down the electrical resistance in your skin, so don't go playing near substations that say "high voltage" thinking you'll be safe.
Extremes in either value (voltage or amps) can invalidate the rules above, so don't let them override common sense. Extremes in either value can also create hazards that are not directly related to biological electrocution or device failure, namely overheating, burns, and/or fire.
So, as long as your charger is outputting around 5V, you will not fry your phone. The more amps it can put out, the faster it will charge the phone, provided that the phone knows it's plugged into an AC charger.
Yesterday I used the stock Samsung charger with my LTEvo cable (USB 2) for about an hour and my battery percentage went from the high 60's to mid 90's. I thought maybe that USB3 cables had a higher gauge of wire to allow higher current, as the stock N3 cable is bulkier than a USB2 cable, but it looks like I was wrong, and USB2 cables can safely carry it.
