Heat oil in a pressure cooker over medium heat; brown pork tenderloins in the hot oil, about 5 minutes per side. Distribute sauerkraut around the pieces of pork and pour in water and apple juice; sprinkle with fennel seeds.
Cover pressure cooker and bring to full pressure; cook for 15 minutes. Remove from heat and release the pressure according to manufacturer's instructions. Place potatoes into the cooker, reseal, and bring back up to full pressure over medium heat; cook at full pressure for 5 more minutes. Remove from heat, release pressure, and serve.