Try to get one that outputs a pure sinewave rather than stepped, some power supplies dont like the stepped variety. I use a APC Smart UPS 1500 that has my external drive, iMac, router, printer speaker system with amplifier (for iMac) and desk top light all plugged into it and its one of my best investments for protecting my iMac from brownouts and power failures.
Buy the biggest, longest run time, from a known Good Manufacturer that you can afford.
As you can use it for other things, peripherals DSL/Cable modems, router, external HDD and other devices, along with giving you more time to shut down, close opened files and programs, before the battery power runs out.
I think the APC ones are USB 2, but be aware if you plug a USB 2 into a USB 3 port of the new iMacs it will set that port at USB 2 speeds the first time you use it.
Only you can work out what size UPS you need, a 21.5 inch iMac does not use much power, but its what else you connect. APC have a great helpline so give them a call. I went for the biggest I could afford for long term expandability, only you can decide what you need hence shootist007 saying get the biggest. When the power goes off I can browse, print, listen to music for a good long while when everyone else is in darkness, also as has been stated you need one that alllows you to shutdown in good time too.
The Mac need a Battery Backup for full protection. Personally I Never connect a UPS to the computer by USB connection as when I am away from my computers they are turned off so if the power goes out while I am out of the house I don't care. what I want and need is if I am using the computer and the power goes out I want Time to Finish what I am working on, Save that, Close the program/s and Shut the system down properly. If I'm sitting at the computer when this happens I certainly do not need the USB system making those decissions for me or Popping up some warning getting in my way.
YMMV if you are the type to never shuts the system down and just put it to sleep for months on end.
Thank for all replies !
Is there a USB specifications that need to "match " the iMac specifications ?
I don't know what the iMac need to be full protect ...there are lots of numbers to check ...
Right there is No Facts supporting either Sleep or shutting down has any effect on hardware or software longevity.
As to Best, like you said that is your Opinion and mine is completely 100% the other way.
To each their own.
I never shuts the system down, I learned that Sleep Mode is best for my iMac ...
But that's only my opinion ...
Please see their answer regarding my question :
Thank you for contacting APC’s Customer Care Team. We are here to ensure that your query is resolved as quickly as possible. Please find our response to your query below.
Dear Mr. Z,
Thank you for contacting APC.
The compatibility of the UPS with an OS is dependant on the installed management software the UPS communicates with.
1. BR900GI - PowerChute Personal - no compatibility with OSX, please find the compatibility chart below:
2. SUA750I - PowerChute Business Edition - no compatibility with OSX, please find the compatibility chart below:
Alternately, if you install a network management card (AP9630 or AP9631) in the SUA750I, it will be able to communciate with the PowerChute Network Shutdown software. This is compatible with Mac OS X Server 10.7.2 x64:
Please let me know if I can assist with any further info.
<Personal Information Edited by Host>
Well all of that is for the software that can control the Shutdown of the computer when there is a power failure. That software might also have other features for monitoring the UPS itself. But that does not mean an APC UPS won't work with a Mac computer. It would still supply power to the computer when there was a power outage but it would be up to you to shutdown in a timely manner as not to run out of battery backup power.
If APC doesn't have software for Mt Lion I doubt you will find any other UPS manufacturer that does supplies software specifically for OS X Mt Lion. It's just to small of a Market Share for them to bother. Maybe for their LARGE UPSs for server environments, as stated, but not for personal Mac computers.
Good Luck in your search & Best Wishes.