In a deep pot or a wok, heat oil until it registers 350 degrees.
While wontons are chilling and oil is heating, place vinegar, soy sauce, sugar, ginger, and garlic in a small pot and bring to a boil, stirring to dissolve the sugar. Once sauce reaches a boil, lower to medium heat (still maintaining a rolling boil, but mixture shouldn’t come close to boiling over) and continue to cook for 15 minutes to reduce sauce. Remove from heat and cover to keep warm.
Remove baking sheet from fridge. Place a cooling wrack on a different baking sheet and line with paper towels; position near pot of oil.
Once oil registers 350 degrees, carefully drop in 3 rangoons at a time. Fry for 40-50 seconds, or until edges are golden brown and the rangoons lose their raw look. The overall tone will be a light-medium golden brown except for the edges. Remove using a slotted spoon and place on prepared baking sheet. Repeat with remaining rangoons, cooking just 3 at a time. Adjust heat accordingly if rangoons are browning too fast or too slow.