prince_13 :
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/