ESS technology enables select UPSs to achieve an industry-leading efficiency level of 99 percent, even when lightly loaded. Using ESS, the UPS intelligently adapts to utility power conditions while supplying clean power to the connected equipment.
VMMS technology optimizes overall system efficiency even at low load levels. With VMMS, the UPS system sets redundant power modules to ready state, enabling the remaining power modules to drive the load with higher efficiency. When the load increases again and more power modules are needed, the system immediately shifts the load to additional modules.
Eaton VMMS Brochure (pdf)