Determining the input and output connections is a very simple--but critical--part of the UPS selection process which can cause trouble during installation. How will the UPS system connect to the utility supply (input)? How will the devices connect to the UPS system (output)? The problem is that connectivity types vary so widely, and many people are unable to identify even the most common plugs and outlets. Because of these limitations, many customers will either overlook this part of the selection process entirely or will simply make an educated guess or assumption. If one guesses wrong, one will have to return the UPS system because they can not connect the device to the UPS or can not connect the UPS to the wall outlet. Examples abound of people who have installed racks of UPS systems only to discover at the last minute, with cords in hand, that only guessed wrong on the type of wall outlet they had.