Although the two terms are often used interchangeably, there is a difference between UPS and Inverter. The UPS is an electronic device which has a rectifier for providing backup power to a device when the mains supply fails whereas the inverter simply converts DC into AC. Another major difference between the UPS and inverter is that the switching of UPS from the main supply to the battery is immediate (taking only 3-5 milliseconds) whereas in an inverter the switching from mains supply to battery takes a little bit longer (100 milliseconds).