I don't know much about other brands, but I have a HO alternator built by Dominick Iraggi. It's capable of 120 amps at idle (700-800 rpms) and 180 amps at driving speeds. The pulley size makes a huge difference. My alt came with a custom pulley, but it was too wide (had 5 grooves) and wouldn't fit in my car. I temporarily used the stock pulley, and the alternator did not perform well at idle. I mean, sometimes my idle would drop to near 0, and the battery lights would come on! Dominick made a new pulley, which was the same as the original one he made except that it had 3 grooves instead of 5. After installing this one, the alt has kicked arse.