John has a Mac Mini with a USB hub, but he can't charge his iPad with it. Leo says that the iPad requires 10 watts to power and re-charge it. Standard USB ports have about 5 volts, but the amperage varies. Apple broke the standard for charging with the iPad. The older ports won't charge iPads because they don't get 10w or power. Apple's own chargers work fine, and if he has a late model iPad Air, he should be able to. But for now, get an 11w charger and that'll do the job.