I have a MacBook Pro 13" Mid-2012. Charges fine. But while using it with AC power adapter, and connected to an external monitor, the AC power randomly cuts out (stops charging, cord light goes out, monitor shuts off) and starts running off of the battery. Then just as suddenly AC power turns back on. 10 minutes later, an hour later, the AC turns off again. Tried PRAM, SMC reset, Used different power adapters. Any thoughts out there about why? and cure? Many thanks in advance.//jasko