The alternator on my big rig won't run a 12k winch at idle, or anywhere else for that matter.
As an example, big rigs will normally run @140 amp alt. but have 4 batteries with 1000cca each. See the point I am making?
The winch uses battery power. The alternator just keeps the battery topped off.
A high quality battery and a regular alternator will do just fine, I have never replaced an alternator due to winching but always run a quality battery.
If you want a higher output alternator, then fine, but never expect it to run a winch.
1998 XJ on 37's.JK Rubi axles with chromo shafts and ctm's, 4:1 transfer case, etc etc etc.The Cherylkee....
2003 Range Rover HSE, 4.4 Quad Cam.
1998 Range Rover 4.6 HSE
2000 4.7 4WD WJ with a rebuilt motor.
4.3/700r4/new frame buildup (YJ)....
Years to gain the hands on experience, and offer it freely.
Minutes to gain the knowledge from the internet, and quote it just as freely.