Unless the return pump(s) is/are very large, a UPS should run them okay. A Mag 9.5 draws about 110 watts, which isn't all that much.
However, remember that UPSs are designed to run a computer for enough time to safely save files and shut it down. A UPS at full load capacity is only rated for a few minutes (no more than 7-9 minutes), so to mitigate that, you need to get a much larger UPS.
How to Size your UPS
The first thing you need is the wattage of the return pump. Some pumps say this straight out, others list the amperage. To get wattage, multiply the amperage by 120. For example, a 1.4 amp pump draws 168 watts.
In order to get about an hour's runtime, you need to upsize the average UPS at least 4 times over. So to run that 168 watt pump, you need a UPS that can supply at least 672 watts.
To get two hours, figure 7 times over.
Finally, convert the wattage. To estimate the VA for a given wattage, multiply by 1.43. 672*1.43 = 961VA.
Get the next size up UPS = 1000VA.
A decent 1000VA UPS should cost between $100 and $200. You don't need anything other than a basic UPS at this rating. None of the advanced shutdown or software management features are needed since you aren't running a computer.
Remember to test your UPS at least a few times a year. Only the very best (and most expensive) UPSs warn you of battery failure before the batteries are almost totally dead. You don't want to discover that your batteries need changing during a power outage!
One final word of caution... one poster here talked about someone he knew that connected several UPSs, one behind the other. This will often not work. UPSs don't put out perfect household current, they put out power that a computer power supply (which believe or not is less picky than a pump) can deal with. UPSs themselves often don't recognize this power, so if one UPS is being supplied by another one on battery, it will kick the second one onto battery and so on down the line until just one UPS is left running your stuff.
. that's what i had to do with a 6 hr power outage last fall.
