Data centers are under increasing pressure, both from customers advocating for greener operations and investors advocating for more profitable operations, to improve energy efficiency. Major UPS manufacturers, including Eaton, General Electric and APC, have introduced proprietary ‘eco-modes’ on their UPSs, which, when activated, can achieve 98.5% to 99% efficiency.
This is a great selling feature.
But a study by Schneider Electric shows that eco-mode is rarely enabled, despite the ensured (and considerable) cost savings. Why? As the study’s author states, “the use of eco-mode entails risks.” While computers and servers are actually relatively resilient relative to power variations, data centers are more complex and “less predictable in their response to infrequent and unusual power events.” 
To work as advertised, eco-mode-enabled UPS systems need to be fine-tuned per installation. This fine-tuning is expensive and tricky. If sensitivity triggers are set too high, the system will switch too frequently, causing significant wear and tear; if set too low, damaging surges and sags can transit before the system reacts.