The MINIMUM I would recommend is a 550W (quality) PSU. I strongly advise a quality 650W PSU.
*The recommendation of a quality 380W PSU for the specs you gave (GTX770 etc) are completely ridiculous.
The scope of explaining why is a little complicated. I'm an electronics Technician and studies Power Supplies and have read a lot of articles on this. A quality PSU with sufficient Wattage will lost longer, be more reliable and be less noisy. FAN PROFILES tend to keep the noise level low until about 50% load.
There are MANY PSU's that have questionable quality and will cause various issues so read reviews and customer comments.
nVidia states that a minimum of 42 Amps on the 12V rail is required. That's 504Watts just for the 12V Rail alone that would be required to make 42 Amps. You can risk running with a smaller power supply if you want but don't blame nVidia if something fizzles out.
really? because my friends say i should get a 600w psu because the 770 takes one 6 pin and one 6+2 pin
Listen to your friends. They obviously have a better idea on what's actually required. Get a good quality Power Supply Unit that is at least 600W and has a built in 6pin & 6+2pin PCI-E power connector. Pulling too much power load through a device that is not built to handle it can ultimately result in catastrophic failure (short, fire, etc). Not to mention it may simply not allow the computer to run properly.
The Power Supply is the LAST place in your computer you want to skimp.