Hi guys, thx for those replies, I appreciate it very much. Got some questions:
1. do I need sine wave? I mean, I read a lot of articles saying that i really need sine wave, othervise the iMacs power supply will make some strange noise during blackout (time when it is supplied from the batteries) eventually, UPS without sine wave (with approx. sine) may damage iMacs power supply! Is that true?
2. do u have any experience with that strange sound of the iMacs power supply using yours UPS (nad which one do u use with iMac)?
3. which one should i choose:
a)
http://www.apc.com/products/resource/include/techspec_index.cfm?base_sku=BR550GI
b)
http://www.apc.com/resource/include/techspec_index.cfm?base_sku=be550-fr
c) CyberPower Intelligent LCD Series PFC 900VA
d) different cbyer power solutions?
and why?
Again, all i need is few minutes during blackout to turn off iMac properly and all time protection (all time iMac is being used) against overvoltage or whatever happens there with electricity (I am not expert, dont know what may happen

And of course, i must be sure that UPS wont damage my beloved iMac
Last but not least, money is concern.
Thx very much for any advice.