Whisk water, ketchup, sherry, hoisin, sugar, and ginger in medium bowl. Pat pork dry with paper towels and season with five-spice powder, salt, and pepper. Heat oil in large nonstick skillet over medium-high until just smoking. Cook tenderloins until well-browned all over, 5 to 7 minutes.
Reduce heat to medium. Add sauce mixture and cook covered, rolling tenderloins occasionally, until meat registers 145 degrees, about 10 minutes. Transfer pork to cutting board, tent with foil, and let rest 5 minutes.
Simmer sauce and any accumulated pork juices until thickened, about 3 minutes. Slice pork and transfer to platter. Pour sauce over pork. Serve.
Notes
Five-spice powder is a combination of cinnamon, clove, fennel, star anise, and Sichuan peppercorns. You can substitute with cinnamon or garam masala.