real USB ports are power limited to 500mA and can shut down if the load is not smart enough to shed the big drain (charging)
You need a USB style charger with a 1 to 2Amp port.
BTW some of the cheaper ones will charge your device, BUT also emit enough EMI that wireless devices (phones, WiFi) have 'reliable' connection issues.
Turn on a Radio (playing a station) in the room. Now plug in the charger.
If you notice, you got problems
