Do you mean the chargers? No, they're all ok as long as they're on 5 volt chargers, which is standardized among USB devices.
Incidentally, current (amps) * voltage (volts) = power (watts). Since the iPad and iPhone both require 5 volts, the spec that makes the difference is the current (amps). Higher or lower current won't hurt the device, but lower current will just not charge it. So if you're buying a charger to use with an iPad (or even an iPhone and iPad), make sure it provides at least 2.1 amps (at 5 volts, which is pretty much a given). If it doesn't specify, make sure it at least says it was designed for the iPad.