An uninterruptible power supply (UPS) can be used with XVR as long as the mains pre-requistes for the XVR are maintained.
Alternatively a kinetic buffer (see e.g.https://docs.automation.boschrexroth.com/doc/533721585/ba1n-kinetic-energy-buffer-project-planning-manual/latest/en/) or additional capacitances may be used for short time (up to several seconds) bridging the loss of mains.
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