It has great reviews because it was once quite powerful, but today's smartphones and tablets need a lot more juice than they can deliver. Even when using the stronger 2V output, my smartphone batteries are slowly draining instead of charging. What you're looking for currently (in 2018) is 6.8A, not the 3.1A provided by this device (btw this is the total for all ports; this will never give you more than 2A from give to a single port).
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