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I want to charge my tablet on the wall. And I have a charger behind the tablet and connected 2 wires to vcc and gnd, the same pins as usb female, it turns out that I can't have more than 10 mA. If I connect with usb cable I get values like 2000mA. Shouldnt it be the same? Is it because of the shield? Should I short the shield to GND?