I was looking into this a few weeks ago also. When I browsed the web places said the oem one is 110-120. But I talked to singer alts and He checked his sources and he says our stock alt on the 2010 focus is a 150amp alt! I was going to order a HO also but he didn't have a case that would fit our model.
2 Sundown X10's in 2.5cuft Net tuned to 31.65hz
SKAR SK-1500.1d, SKAR SK-85.4
Lots of Audio Technix 0 gauge
XS Power 1200,XS Power XP3000
I murder lowssss