What is the difference between Sarva Pitru Amavasya and regular Pitrupaksha Shradh?

Regular Pitrupaksha Shradh is performed on the specific tithi (lunar day) matching the day an ancestor passed away — so it honours that one ancestor specifically. Sarva Pitru Amavasya is an all-encompassing ceremony whose Sankalpa covers every ancestor in the entire lineage — both paternal and maternal, named and unnamed, known and unknown, across all generations. It is the final, comprehensive offering of the fortnight.