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Will the 10W USB Power adapter (I got w/my iPad) hurt my iPhone 4S?
No. The iPhone will draw as much power as it requires to charge its battery. It cannot draw too much, nor can it draw more than the adapter is capable of providing.
Conversely, you may also use the iPhone 4S charger to charge the iPad. It will just take longer to charge than it would with the iPad's charger.

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