Not really sure how an alternator would be the cause of a car stalling at a stop. Only thing is the battery is so bad that the computer is not getting power. I would guess, because you did not give much information about this, that you need a good tune-up. Spark plugs, wires, air filter, fuel filter, maybe even coil. Run some good carb cleaner through it.

On the chance it is a battery/alternator problem, you can check with a volt meter to see what the batter is putting out, should be just over 12 volts DC. When the car is started the output should jump up to 13 or low 14 volts.

GL

I'm guessing the reason you changed the alternator was electrical. Maybe your battery kept going down. Find and change the bad charging system fuse. You know the alternator is new. The other thing you need to do is an OBD2 code check. The car knows what its problem is, but it won't tell you if you don't ask. Pay attention to the trouble codes that come up, but also get help with the reason certain codes are there. If you want to just start changing parts without knowing their condition, you might as well hand me a blank check, because you're going to pay for a lot you don't need.

When they changed the alternator they neglected to put something back properly, it happens. Take it back and the guy that worked on it will probably know pretty quickly. I suspect he's left the air intake boot loose and the mass airflow sensor isn't getting the proper signal, that or a simple vacuum line.

sounds like fuel issue. replace fuel filter first and try that. if that does not fix it then check fuel pressure and if the pressure is low unplug fuel regulator see if the pressure jumps up if not then replace fuel pump but most times its just the fuel filter