<https://audiophilestyle.com/forums/topic/4735-lengthy-primer-on-ac-with-some-thoughts-on-reducing-the-computer39s-impact-on-yours/#comment-56347>
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"I would strongly advise not to use regular UPS devices on a high end audio system.  These units are made without regard to quality of their output, and are generally just made to keep critical computer system components running in the event of a power failure.  Here are some of the problems inherent in typical UPS devices: \nIn AC mode: \nPoor quality wiring and connections, which will introduce more noise on the AC line, and will raise the AC line's impedance (resulting in a drop in system dynamics).  Some UPS also run in an always on mode, where the AC output is always generated by the switching output stage; if this is the case, then all of the below problems will apply all the time. \nIn battery mode (this is where it really gets bad): \nNot enough battery capacity to achieve low output impedance, resulting in poor system dynamics. \nMost UPS devices use a switching output stage, built with very little regard to noise performance-so running from a UPS, on battery power, has much more noise than plugging directly into the wall with no power conditioning at all. \nMost UPS devices output a square wave, rahter than a sin wave, this means thta they have huge amounts of harmonic distotion on their output.  If you must use a UPS, definitely get one with \"true sin wave\" output (more expensive) but note that the output is still highly distorted, with typically around &gt;20% distortion, still way too many harmonics to expect decent performance from an audio system. \n  \nThere are very expensive lab grade UPS supplies that can avoid these problems, but one will find that these UPS cost more than the most expensive audiophile products. \n  \n"
<https://audiophilestyle.com/forums/topic/4735-lengthy-primer-on-ac-with-some-thoughts-on-reducing-the-computer39s-impact-on-yours/>