There is no powerful spell by itself, the PERSON who uses it must be powerful in order to be successful. Its like giving a high-potentional weapon to an inexperienced person who can't aim, he/she won't be able to use it correctly. There are useful spells in the JoS site, some links...

The dedication ritual has to do with protection, not power. People who are not dedicated are not under Satan's protection and don't have a Guardian Demon. And the ones not under Satan's protection usually have serious angelic attacks and negative experiences when they get powerful, because...