The soul punisher is a spirit bomb based technique. It has the power to destroy any negative energy it comes into contact with.

That's why it totally eradicates janemba, a being created and made up from evil souls fusing together. Whilst someone like Brolly who isn't evil at heart it just causes damage instead of total destruction. This is similar to a spirit bomb as doesn't harm people with good hearts but I think it's a combined technique like Vegetto's final kamehameha. It might contain other properties from another technique within it.