Will you please provide some information on these groups and the extent of their adherence to beliefs of Ahl As-Sunnah Wal-Jamaa‘ah (the mainstream people of the Sunnah): The Ansaar As-Sunnah Al-Muhammadiyyah, and the Usooliyyoon?

All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.

With regard to the Ansaar As-Sunnah Al-Muhammadiyyah, it is an Islamic group that follows the path of the Salaf). It was founded originally in Egypt, and then it spread in other countries to call for Islam based on pure Tawheed (Islamic monotheism) and the authentic Sunnah, and to purge Bid‘ahs (innovations in religion) and myths as a condition for the return of the caliphate and revival of the Muslim nation.

The Usooliyyoon, on the other hand, is a term used nowadays to refer to people of the truth who adhere to, call, and fight for its cause. Earlier, it was applied to those who studied Usool Al-Fiqh (Fundamentals of Islamic Jurisprudence). This term is also attached to fundamentalism, a protestant movement that arose in the West in the 19th century. 

Allaah Knows best.