The fragrances typically referred to as "powerhouses" here are fragrances from the late 70s all through the 80s that are very strong and often feature prominent notes of pine, patchouli, musk, and oakmoss. Some examples of the style that are widely available for testing are Korous, Paco Rabanne Pour Homme, Bijan for Men, Aramis, Grey Flannel, Quorum, and Versace L'Homme, all of which could probably be found at a mall Perfumania if you want to make yourself familiar with the style.
Some people just use the term "powerhouse" to describe a very strong scent in general though. It's usually used to describe the former definition though.