UPS on DC controlled tables?

I doubt it, Avliviero. DC regulator for motor control is very easy to do and
inexpensive. The technology has been perfected for quite some time. There is
no reason for manufacturer to put in subpar regulator. Unless you have a cheap
TT and your AC line is extremely unstable, I don't think it will make any audible
difference. Besides, if your AC line is so unstable that it will affect TT, I think it
will have a more profound impact to the rest of your system. In order words, if
you have AC line problem, I would address it for the rest of the system before
putting a power plant just for TT.

Sidssp,

Thats a good point.although I suspect the impact of ac on speed control would be more audible than on pre and power amps

Not the same as a UPS but in the same vein, I have been using an upgraded external power supply.

I am using an HP 6200B lab power supply with my DC motor Sota turntable. I bought this because I noticed minor speed variations that my non-audiophile family could not hear. This is a highly regulated DC supply that allows fine adjustment of voltage up to 40 volts. The turntable motor assembly already has a voltage regulator. As others point out, a voltage regulator in a turntable is not necessarily complicated: mine has a standard chip and a few other parts.

There are at least two advantages to the HP power supply: 1. I like the way it looks, and 2. More seriously, it unexpectedly allowed me to diagnose a bearing issue with the turntable. I set the power supply to monitor current draw and noticed a periodic fluctuation. When I turned everything off and rotated the platter I heard a faint rubbing sound that I hadn't noticed before. I disassembled the platter, thrust plate, and bearing, cleaned everything, and relubed. Then I carefully leveled the turntable and gave the platter a good spin. Total silence.

Reconnecting everything again, the speed issue is gone and the meter now shows a much smoother current draw. In summary, I'm not sure that the lab power supply improves the overall sound when everything is normal but it did prove useful, looks very serious, and at the least, allows me to monitor voltage and current closely.