From what I have been able to read, I estimate that the Steam Deck charges with about 60W. With this power bank, you could therefore supply the Steam Deck with power for about 2.5 hours (166.5 Wh capacity with 60W power consumption, without the Steam Deck battery, only via power bank). I don't have a Steam Deck myself and therefore can't say 100% how well this works. But I can charge my laptop several times with it (also consumes ~60W, possibly even more)