As a former instructor I learned real quick to use correct terminology. Since the mid 1960s cars have used "AC generators". In 1960 Chrysler introduced it as the "alternator" and copyrighted the term. In an attempt to standardize terminology the industry uses "AC generator" but we all know what we mean by "alternator". It's the same thing.
12.7 volts in the battery means it was getting charged and you likely have a starting problem and as such, KHLow2008 has pointed you in that direction. In a very rare case there could be one of the two solenoid coils open, (broken), and the higher voltage from the jump-start gets it to work. That can be a tricky one to find. Much more commonly you have a simple loose or corroded battery cable connection that is getting squeezed tighter by the jumper cable clamp. (If I'm right, it will still start with the jumper cables connected to your car only and not the assisting car). There's a couple of different ways to approach that. The fastest is to just take the battery cables off, clean them, and be sure they're tight when you put them back together. If that solves the problem, you have to just assume that was what was wrong. The better but more time-consuming way is to measure the "voltage drops" or to simply measure the voltage at various points in the fat cables going to the engine and to the starter. Voltage drops will identify exactly where the bad connection is so you know you're fixing the right thing. It takes a lot longer to explain voltage drops than to actually measure them so if you want to pursue that route, I'll send you to a page that shows how to do it and interpret the results. All you need is an inexpensive digital voltmeter, and a helper to turn the ignition switch.
Friday, August 10th, 2012 AT 11:21 PM