Take pork loin out of refrigerator and let set at room temp for 20 to 30 minutes. Pat pork loin dry with a paper towel and sprinkle with salt, pepper, and garlic powder. Don't trim the fat.
Set Instant Pot to Saute. When hot, add oil and add pork. Brown pork on both sides, 4 to 5 minutes per side. Press cancel on the Instant Pot and remove pork to a plate.
Add broth to Instant Pot and scrape all bits from the bottom of the pot. Add vinegar, Worcestershire sauce, and brown sugar.
Place trivet in the Instant Pot and set pork, fat side up, on top of trivet.
Secure lid, turn valve to seal.
Set pressure cooker to “pressure cook” or “manual” (depending on model), high pressure, for 27 minutes. Let pressure release naturally (in other words, leave it alone) for 15 minutes before releasing remaining pressure, if any, by turning valve to “vent.”
Transfer pork to a cutting board or plate and let rest for 15 minutes. This step is essential. The internal temperature of the roast will continue to rise as it rests. Check temperature of pork using an instant read thermometer in the center of the roast. It should read 145ºF.
Meanwhile, switch Instant Pot back to “Saute” and simmer pan juices to form a sauce.
Slice pork and serve with pan juices.
Nutrition information is calculated with a 3 pound roast.
Leftover pork can be refrigerated for 3 to 4 days. Frozen pork will keep for up to 3 months.