if the rectifier is faulty, the voltage will be spiking and make the lights flicker.
the car draws it's voltage from the battery normally ( not directly from the alternator ) so a rectifier fault often goes unnoticed for a time till total failure - except with the lights which you can see easily. The thing has probably been going bad for a while and is putting out such a strong AC current now ( instead of the normal DC ) that the battery can't flatten the voltage spikes any more. ie it's about to die on you.
Usually the rectifier is a plug in unit on the back of the alternator itself. But it may be a separate unit in the engine bay as well. You simply buy a new one, unplug the old one and clean up the connections a bit, and plug the new one in.
They aren't expensive, and if you're not sure which bit it is, when the parts guy gives you a new one, click the bonnet open and just look around to find it
I will bet you that you have a rectifier on the back of the alternator ( the most common place ) and that the "new" alternator had an old rectifier on it... either way its duff now eh
