The original uUSB charge standard was 1 Amp but the newer Galaxy fones come out with a 2A charger.
You can use the 2Amp charger on an earlier fone ... the fone only draws the current it needs to charge (1A) and will charge at the normal rate. On a newer fone it will charge faster.
Do not get into the habit of leaving your fone on the charger overnight ... constant charging is not good for LiIon batteries.