Robert Kern, the son of a Baptist minister from Iowa, set up shop with five employees in a garage in Wales, Wis., in 1959 to make portable generators. Early customers for his Generac Corp. included farmers and construction crews. Soon all kinds of people were buying his generators under the Craftsman brand at Sears stores. Mr. Kern diversified his range to include permanently installed generators for homeowners worried about power outages. Generac also developed equipment providing backup electricity for telecom networks, hospitals and other facilities. The Y2K scare yielded a rush of demand, as did hurricanes and tornadoes. In 2006,...