A1-840

Well, there are only a few things in that circuit. There is the charger itself, the connector it plugs into, and the motherboard that the socket is installed on. Most times when there is a problem it's the charger or the connector on the charger cable. Less often it's the connector on the tablet side, which would require a motherboard replacement. Very rarely it's a problem on the motherboard itself, also fixed with a motherboard replacement. If you can test trhe charger or find another one to try you can likely find the problem quickly.

Yes, as long as the voltage, amperage and connector are the same you can use theirs. Typical problems of mismatched polarity or plug size aren't usually found with the micro USB style, since the spec describes the voltage and pinouts. Most manufacturers these days charge at a higher current rating that USB specs for data connections, so the spec allows a special charging mode that gives you the extra amperage, and that's also standardized.