My personal ethos on if an alternator is sized correctly is this.
Start Car -- get to an normal idle.
Turn on ALL electrical items ; headlights , on high beams, fog lamps , cooling fans(all) , heater blowers, satellite radio.
then with your Voltage gauge in the dash -- you should see 14.1 - 14.5v ===(you *are* running a voltage gauge versus a AMP meter hooked up to a pair of wires that could act as welding rods right >? )
you also could measure between the + terminal on the ALT and a engine ground for the same V reading.
You can go as low as 13.9 with all that running, but a good solid 14.1-14.2 is best in my opinion.
Steve