What is the difference between UPS and SMPS?

SMPS is switched mode power supply, it mainly converts AC to DC or DC to DC. 

Where UPS is an uninterrupted power supply, it delivers emergency power to a load when the primary power source is lost. A UPS differs from an auxiliary generator, in that it contains a battery that “kicks in” when the device senses a loss of power from the primary source.

A UPS is typically used to protect hardware such as computers, data centers, telecommunication equipment, or other electrical equipment where an unexpected power disruption could cause injuries, fatalities, serious business disruption, or data loss. UPS units range in size from units designed to protect a single computer without a video monitor (around 200 V-ampere rating) to large units powering entire data centers or buildings. Small UPS systems provide power for a few minutes (enough to power down a computer in an orderly manner), whereas larger systems have enough battery back for several hours. The world’s largest UPS, the 46-MW Battery Electric Storage System (BESS), in Fairbanks, Alaska, powers the entire city and nearby rural communities during outages.