5th level paladin using a greatsword. 10STR No feats or shenanigans, just class features and smites.
Two attacks.
With super double crit luck: 8d6+12d8 radiant (rerolling 1s and 2s)
With Crit and a hit: 6d6+9d8 (reroll 1, 2)
With Crit: 4d6 + 6d8 (reroll 1, 2)
With hit: 2d6 + 3d8...