It is a third Paralympic medal overall for the visually impaired skier, who had recorded two fourth-place finishes earlier in these Games.
In the alpine combined, skiers complete a run of both the super G and slalom, with their factored times combined to determine the final standings.
Simpson and Poth had sat in fourth after the morning's super G, 0.57 seconds short of third place.
But in the slalom, they recorded the fastest time of the day to move up two places as Canada’s Kalle Ericsson and his guide Sierra Smith fell out of contention.
Italy's Giacomo Bertagnolli and guide Andrea Ravelli won gold, finishing 0.65 seconds ahead of Simpson and Poth overall, while Austria's Johannes Aigner and Nico Haberl won bronze.
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