Pierce/prick the potatoes with a fork; all over.
Place the trivet and water into the pressure cooker/instant pot.
Set the ube purple yams down in the cooker.
Pressure cook on high for 20 minutes and natural release for 10 minutes. Note: small potatoes cook for 15-20 minutes and large potatoes cook for 25-30 minutes.
Remove the potatoes from the cooker.
Cut the potatoes in half and add 1-2 tsp butter to each potatoe (optional but recommended).