Unlike earlier iPhone OS devices however, the iPad only syncs over standard USB; it needs more power than that specification can deliver to actually charge. USB 2.0 only provides 2.5 watts for devices to pull in order to recharge their batteries.
The iPad’s power adapter (in the shape of USB; it looks like the old iPhone adapters, or like a mini MacBook power supply) provides 10 watts.
So unless your system’s USB ports were specially designed to put out 10 watts (and most if not all weren’t), you’ll need to charge your iPad using the supplied adapter, and not an iPhone one or a typical PC USB jack. It might take a lot longer to charge it from a standard USB port.
Fortunately, the iPad’s battery lasts a long time.
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