I use a Belkin BU3DC001-12V. It completely replaces the AC adapter that comes with the Tablo.
It is a 12v UPS so it avoids the losses associated with stepping up from 12 VDC to 120 VAC and then back down to 12 VDC, resulting in much longer runtime. You lose the flexibility you have with a standard 120 VAC UPS since this can only be used for 12 VDC devices. They are available new on Amazon, but are quite expensive. They can be found at much lower prices on eBay (new and used).
I have several. I use them on my Tablo as well as my cable modem and router. I use a splitter cable so I can use one UPS to power my cable modem and router. One unit is able to keep both of these running for multiple hours during a power failure. The only significant drawback I have seen with these units is that they do not handle the really quick power blips. The type where the power fails for a fraction of a second. For some reason they tend to reset when this occurs. I do not have many of these, though. Most of my power failures last from several seconds to several hours and they handle these flawlessly.