Uninterruptible power supplies are part of the very dull plumbing in most server rooms, and, increasingly, in many homes.
There are two major types: A standby UPS only powers protected equipment when there is an issue with the line power. The rest of the time, it simply charges its batteries and passes line power on. An online UPS powers the equipment from its batteries at all times, using the line power to keep them charged. Standby UPSes are more cost-effective, but online UPSes provide better power filtering. Probably the most common manufacturer is American Power Conversion. APC started selling UPSes shortly before CDN was born, but it’s a mere infant compared to Tripp Lite, which was founded in 1922 to produce automobile headlights. By the 1960s, it had added power products to its portfolio, and in 1980, it marketed the first UPS for a PC.