Small powersupply to power a ESP microcontroller for example. Small enough to build in a small case or a box. It delivers 600mA maximum on a total load. It is not enough to power LED's but it is enough for a ESP-01 with a relais or a sensor. It is very usefull because it has both currents, 5 volt and 3,3 volt. When you need both you can have it in one supply so it saves precious space.