I don't think of these systems in that way There are several "areas" and ways that I look at this:
1...Battery must be in good shape, not sulfated, or worn out, or with bad cells. "A normal battery."
2...Generally connections and cables must be good, clean, tight.
3...Charging path. The output path from the alternator stud, through the bulkead, ammeter, back out bulhead, to battery. If there are bad connections here, can cause unacceptable voltage drop as well as this kind of nonsense.
4...Field circuit. This is the entire circuit from battery, ammeter, ignition switch, VR IGN terminal, (VR ground), to green alternator field connection, and condition of brushes, slip rings.
5....Components, VR and alternator
AFTER checking the wiring and battery in 1--4 above, then worry about if VR or alternator has a problem. It is possible for field windings, example to rub on each other, become loose, and short together. This will cause ammeter fluctuations, as well as an interesting lightning show in the dark, inside the alternator.
Bad/ worn brushes and slip rings can cause weird problems
And "once in awhile" a bad VR particularly an older MECHANICAL VR can cause flickering.
That generally is how I go about it. Attack the wiring and connections. Then check the alternator, and VR
And, as usual, "new" does not mean "good." New components can be defective, and rebuilds are always suspect
