The details for the Air Gradients show that a power supply is not included. This is now getting to be very common from manufacturers where a device is designed to be powered by a standard 5V supply. Also, especially for lower wattage items, people are likely to have these sort of supplies hanging around or permanent wall sockets (or pass-through mains adapters) that have USB power outputs.
Obviously, if a device is going to be on all the time (like the AG) it will need its own power supply.
It’s a catch 22 situation. If a power supply is included, then the cost of the device will be higher to reflect that. Where the required power supply is a common one, then it is probably better not to include it and let the buyer use an existing one they might have (thus saving them money) or buy one.
Buying a power supply, as has been previously mentioned in the thread, may be a problem. An alternative is for the maker (e.g. Air Gradient) to give the option of buying a power supply separately - a multi-country power supply with different plug heads means that only one type of power supply has to be kept in stock. However, because of sending from abroad, this could make the power supply more expensive than buying a decent one locally.
One advantage of both the indoor and outdoor AGs is that they’re generally not fussy as long as they can supply 5V DC at a minimum 2A or more (the measured current the AG uses is around 1.5A).