Portable power stations come in different capacities. Beyond the "Wattage" being advertised (ie. 200W, 300W, 400W, etc.), the more important parameter to look at is the Wh capacity.

The formula is:
Equipment Wattage (W) x No. of hours of continuous use (H) = Required battery capacity (Wh)

So if your laptop consumes, say, 50W. You can get up to 4 hours from a 200Wh portable power station. That is the best case because the conversion is not 100% efficient. So it's safe to assume that you'll get somewhere around 2-3 hours from running a 50W laptop (and nothing else). In reality, you can get more time depending on whether the laptop is allowed to throttle down (reduce energy consumption) with light use.

Portable power stations are ideal if the outage is relatively short and far in between (to allow for charging time). For longer outages, a small inverter generator would probably be more practical.