Critical systems run smoothly with regular maintenance and reliable tools Everybody knows that consistent, dependable electrical power is critical to any plant's function. But perhaps even more critical is a reliable uninterruptible power supply (UPS) system. UPS systems are the silent partners that just sit and wait until there's a break in power. At that point, the UPS system is the most important system in the plant. It has to be ready to spring into action in milliseconds to keeps things running for anywhere from seconds to hours.