@millercarbon @lewm Thanks to you both for your responses, which confirm I am on the right track.
To clarify, I have a Clearaudio turntable with a 12v DC motor. Clearaudio indicates that their DC power supply is voltage stabilized, yet they sell a separate 12v battery power supply. This suggests the stock power supply has some limitations.
My APC S-20 power conditioner and UPS which I use for computer and video gear has a voltage display that clearly indicates variations from 120 to as low as 113 volts, with changes at seemingly random times. I suspect this may have an effect on the turntable speed, but haven’t checked with a strobe or other device. If I can confirm that is the case, then the question is whether to get a battery power supply like the Clearaudio or a regenerator or similar device that can power multiple devices. The Farad LPS suggested by @millercarbon is for a single device, but is a lower cost alternative to the battery supply. Will it work as well?
As to EMI/RFI, I am confident the Niagara 1000 is doing a good job there, as my wife and I both can discern a very noticeable improvement in resolution and detail with the digital sources, pre-amp and amp plugged into that unit.
Any further thoughts you may have are sincerely appreciated.