Actually, the diodes are there to produce a pulsating DC voltage. As you all have been wondering why they are called alternators, it's because they produce an alternating current. The diodes rectify this voltage and thus produce a pulsating DC voltage. The size of the stator windings determine the current the alternator will produce. Thus your higher rated alternators have somewhat larger stator winding. If my college physics serve me, the length of the windings, RPM's and strength of the field determines the voltage and the gauge of the windings and the rating of the diodes are the limiters on the current produced. Also, most quality alternators produce a three phase output, which is to say there are three sets of identical windings in the stator, one end of each is grounded and the other end is attached to a rectifying diode. So the end result is a smooth pulsating DC voltage.

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Jeff Lawrence
1989 300e
2000 Dodge Grand Caravan SE
No matter what you fix, there will always be something else to fix..
"Warranty" is just another way of postponing the inevitable.