Get ready for all the "you need sine-wave UPS" posts ;)
If you insist on a UPS, all you need is one that will send line voltage when deactivated, and switches over to battery only when the power goes out.
BUT, I'm not convinced you need a UPS to begin with. Cutting power to your PJ does nothing to harm it. The harm comes in trying to cut it back on with a hot bulb. My Panasonic 75u remembers the last state, and will actually power back up in the cooldown mode before reigniting the bulb. As long as you don't try to power down/up with a hot bulb, IMHO, your money is better spent towards a conditioner/surge protector. Of course a quality UPS can do the above also, so if you're dead set on a UPS find one that does all three jobs :)