In a large bowl, combine the soy sauce, white vinegar, water, crushed garlic, black peppercorns, and bay leaves. Add the chicken thighs to the marinade, ensuring the chicken is well-coated. Cover and marinate in the refrigerator for at least 30 minutes (or up to overnight for better flavor).
After marinating, remove the chicken from the marinade. Reserve the marinade for cooking.
In a skillet or Dutch oven, heat the vegetable oil over medium-high heat. Once hot, add the chicken pieces skin-side down and sear until browned, about 5-7 minutes. Turn the chicken to brown all sides.
Once the chicken is golden brown, pour the reserved marinade over the chicken. If desired, add sugar for a hint of sweetness. Bring the mixture to a gentle boil.
Reduce the heat to low, cover, and let it simmer for about 30 minutes, or until the chicken is cooked through and tender. Stir occasionally and adjust seasoning with salt if needed.
Once cooked, serve the Chicken Adobo hot over cooked white rice, spooning some of the sauce over the top.