I never had need for one of those, but they are common on police cars and ambulances. More amps than you need is no big deal as the alternator automatically adjusts to put out exactly what is needed. I have a problem with those gizmos that increase the output voltage, as they can cause problems with the computer and some accessories, and can cause damage due to over-voltage.

 

if that actually works. it increases volts not amps. the basic formula is watts/volts = required amps... 1200watts/12volts = 100amps.
it fluxuates depending on quality of amps and ohms, and etc. but thats basic formula. lets sat that thing increases volts to 13(cuz basic is actuall 12.4-12.6) 1200watts/13volts = 92amps requires. not a significant decrease. !!!BUT!!! on altinators, when you increase volt output, you decrease amp output, and vise versa.. if you make a alternator put out, lets say 15volts, and test it, at 2500rpms, and it's spose to do 105 amps, it'll prolly be doing about 85/90. but vise versa is true also. 10volt alt will make about 125amps(this is based off from 105amps @ 12.4 volts)

the reason they use higher volts in alot of emergency vehicles, is cuz, they need the "sudden" burst of electricity. and volts is " the potential" where amps is the "power" for sudden bursts of power, they dont so much have to worry about amps, cuz they have a battery, that will be charged by alt, after the objects are shut off...

http://www.bcae1.com/ thats a good site to learn from, but it's long. good 3 or 4 hours of reading at least.