Originally Posted by
cepheid
this is because the MacBook Pro is (somewhat of) a power hog and will blow out an EmPower port using a generic adapter. The Apple-branded adapter triggers the MBP to stop charging the battery (power is used for operation only), allowing the computer to operate without tripping the breaker.
Not sure if this is true with EmPower ports too, but with the AC outlets on p.s. flights if you have a battery that is close to fully charged the breaker doesn't trip when you use the laptop. It also doesn't trip if the computer is off/standby but the battery is being charged.
When I need to use the laptop with low battery (but can't wait till the battery charges up enough to draw less current) I just take the battery out.