While most well-made USB-C chargers can charge a Nintendo Switch in portable mode, AmazonBasics made an AC charger that can run the dock as well, and it’s just $14 right now, or half the price of Nintendo’s.
It has the exact same 39W output as Nintendo’s first party charger, plus “short-circuit protection, over-temperature protection, and over-voltage protection to protect your device.” Perhaps most notably, its cord is about a foot longer than Nintendo’s, so it should give you a little extra flexibility when setting up your dock or playing in bed.