The Smurfiest Wizard Ever!
It never maxes out. The most we've had to date was 4d20s (original d20, plus two sources of advantages, and elven accuracy adding a 4th die).Do you go so far as to roll double/triple advantage or does it all stack and cancel out but the max is still one advantage or disdvantage?
Ex. if you have three sources of advantage (not easy to get, but possible) and one disadvantage, net is "+2", so you get both d20s for advantage still (total of 3d20).
We just think of them as +1/-1 for adv/dis and add it up.