There are a bunch of threads on the forum with a ton of different solutions to the problem. It doesn’t seem to be any one fix is a silver bullet. For mine personally, I haven’t had an issue since I ran a ground cable from the spindle mount to my electrical box. I’d say try some other stuff before buying anything.
That said, if you get a UPS to try and solve the problem, it will need to be a “double conversion” type, which are more expensive. This means it is always taking in AC, rectifying to DC and charging the battery, and then inverting power from the battery back into AC. The cheap units are typically “line interactive” meaning they normally run on AC, and have a static switch inside that transfers to battery when power is lost. So if is normally running on AC, it won’t help with your problem.
I would agree on power draw. Thats why I figured router would be run off of standard outlet. I am doing that now. That outlet goes back directly to my main panel. S3 controller and tablet run off power from my sub panel. My concern is not running on power loss, but providing better isolation from power blips as the control board seems to be pretty sensitive.
I added a marine grounding buss to my setup. Mines a little more complicated then average due to my 240v spindle setup. I have had zero disconnects with it. And I run both my spindle power and motor feedback through the same drag chain. I have my 120v, 240v, Shapeoko drive board, VFD, spindle, and base for my Shapeoko all tied together on it. That way everything is on an even playing field