To understand how these coolers work, we first need to know a bit about how air conditioning does its thing.
Conventional air conditioning units create cold air by transferring heat from the warm air taken in from the room to refrigerant coils, cooling the air that is circulated back into the room.
One of the by-products of this process is that moisture present in the air condenses on the cold coils inside the unit. That condensation builds up, forming large droplets of water that drip down into a catchment area, which is generally a deep tray.
In self evaporating equipment, that condensed water is reused by evaporating it off the coils. That aids in the cooling process, just like evaporating perspiration from your skin helps you to cool down when you feel a breeze.
The evaporated water vapor is then exhausted out of the unit through the pipework to the outside along with the hot air that is also produced by the heat exchange mechanism inside the unit.
Portable AC's do all this inside a single unit and vent off the hot, moist air through its flexible hose that is connected to a window kit or wall outlet.
Window AC are already mounted in a window so have no need of a vent hose, expelling the exhaust air directly to the outside.
Mini-split or central AC systems expel the hot, moist air through ducting or pipework to an external condenser unit which releases the unwanted hot air into the outside atmosphere.