Try checking all the fuses again, that box is probably right. I've owned 4 G.M.'s and they all used one fuse for multiple devices (i.e. cigaratte lighters and a radio).
There should either be some description on the fuse box, cover, or owner's manual that tells where the correct fuse is.
If not you can go ask a Buick mechanic or buy a correct Chilton's manual for the car.
Or you could re-wire the lighter with a 10 amp inline fuse.