This material discusses in detail the fuse diagrams of the Buick Cascada (first generation): 2015, 2016, 2017, 2018, 2019 release.
Fuses #7 and #6 in the passenger compartment are responsible for the cigarette lighter and 12V power sockets.
In the luggage compartment
Located on the left side of the trunk, behind a cover.
In the passenger compartment
Fuse box located behind the glove box in the instrument panel.
In the engine compartment
Located near the battery, behind the plastic cover.