Cook the bacon in a Dutch oven over medium heat until it renders its fat and turns crisp, 7 to 9 minutes.
Transfer half of the bacon to a plate and cook the onion in the pot until translucent, 4 minutes.
Add the green beans, broth, salt, pepper and sugar and bring the liquid to a boil.
Lower the heat, cover partially and simmer until the beans are fully tender but still hold their shape, 40 to 50 minutes.
Uncover for the last 10 minutes if more than 1/2 cup liquid remains, stirring once so the bottom does not scorch.
Stir in the vinegar, scatter the reserved crisp bacon over the beans and serve with a little pot liquor.