what is an automatic voltage regulator pc ?

The AVR is a modified Harvard architecture 8-bit RISC single-chip microcontroller, which was developed by Atmel in 1996. The AVR was one of the first microcontroller families to use on-chip flash memory for program storage, as opposed to one-time programmable ROM, EPROM, or EEPROM used by other microcontrollers at the time
 
While RealGamingwithJohn's answer is 100% factual, it has nothing to do with the question.

The type of AVR you are asking about basically cleans the power that's feeding your PC. It regulates it to pure 110V or 220V and prevents surges.
If you are in an area where you experience bad power or power surges, I would highly recommend an AVR or a good quality UPS.
Good UPS's have built in AVR.
 


so it protects my pc from brownouts and blackouts ? even though with no power my components is safe ?
 


Yes, it will help protect your pc (or anything else connected) from power spikes that can often happen during or just after a brownout / blackout.

A UPS helps even more, because it will give you a few minutes after the power fails to shut down your pc.

An AVR is a better version of a surge protector, see here:
http://www.howtogeek.com/166938/protect-your-gadgets-why-you-need-a-surge-protector/
 


even this kind of avr ?
http://s83.photobucket.com/user/masterkulas/media/Computer%20Hardwares/avr500wfront.jpg.html

 


i dont think avr have a good brands . in my country apc is the only good brand but they dont make a avr
 


that model is already out 🙁