It's taxing the wiring, more amps = more heat, more heat = more resistance, more resistance = a BUNCH of voltage drop.
Stock period mopar alternators SUCK at idle as well. So if you are idling, fan turns on and saps whatever energy out of the system, there is not much else to keep up. If you have a voltmeter, watch it when the fan turns on. A lot of engine electronics will not function at low voltages. Voltage drops below the point that a igniotn box must see, done- shut off.
