Some players still prefer 9V batteries to power their pedals, but if you're looking to invest in a board, you'll probably want a dedicated power supply. Power supplies are a lower-maintenance, cost-effective and eco-friendly solution compared to batteries.
When shopping for a power supply, the most important factors to consider are its number of outlets and whether each outlet is isolated or not. If a power supply does not feature isolated outputs, each output shares power from the same circuit, which can lead to unwanted noise in your signal chain, as well as power outages for your entire board, rather than one pedal going out at a time.
Also, consider the voltage of each outlet -- many power supplies contain a mix of 9V and 18V outlets, designed to feed different pedals, or to make overdrives behave in different ways. If you're unsure, you'll want to check your pedals' specifications to make sure they're compatible with the outlets provided by your power supply. Also important to note is the size of the power supply itself. If a supply can't fit under your board, you'll have to make room for it on the surface.