The best way to figure out if your PSU is not supplying the correct/enough juice would be to purchase a PSU tester. Great tool to have on hand.
https://www.google.com/search?q=PSU+tester&oq=PSU+tester&aqs=chrome..69i57j0l5.2239j0j4&sourceid=chrome&es_sm=122&ie=UTF-8#q=PSU+tester&tbm=shop

What is the current power output (in Watts) listed on your PSU? If you list your hardware in your post I could figure out how much power is being consumed (roughly).
Or you can visit http://extreme.outervision.com/psucalculatorlite.jsp and get a rough average estimate yourself.
Answer from Richie086 on Stack Exchangei got a new one, a corsaire 650 which will replace the 450w one
but i would like to make some kind of stress test on them, with gpu+cpu
what is the best software to monitor the use of my psu ?
PSU monitoring in HWiNFO (supported PSUs and available readings) | HWiNFO® Forum
need software to monitor PSU voltages
PSU temp monitor | Overclockers Forums
Power supply with monitoring software?
Videos
The best way to figure out if your PSU is not supplying the correct/enough juice would be to purchase a PSU tester. Great tool to have on hand.
https://www.google.com/search?q=PSU+tester&oq=PSU+tester&aqs=chrome..69i57j0l5.2239j0j4&sourceid=chrome&es_sm=122&ie=UTF-8#q=PSU+tester&tbm=shop

What is the current power output (in Watts) listed on your PSU? If you list your hardware in your post I could figure out how much power is being consumed (roughly).
Or you can visit http://extreme.outervision.com/psucalculatorlite.jsp and get a rough average estimate yourself.
The PSU provides the rest of your hardware power, granted, but how the rest of your devices regulate that power depends on the motherboard.
One of your screen flickering might be due to the monitor itself, the connection from the monitor to the dvi/vga/hdmi slot, it could be due to bad drivers, or a faulty video card.
I've seen problems with cell phones not getting the "correct power" due to multiple reason, OEM chargers, different USB version (1.x, 2.0, 3.0, etc) so it's hard to say really.

USB Wiki
Is there any other PSU brand that has something similar to Corsair HXi series and their Link software?
I really like the way you can see the wattage, efficiency, and create fan/temp curves, but unfortunately, this is the second HX850i I got that has issues and I’m not sure if I want to take the risk and go over 30 days return window with the store and deal with the manufacturer directly (the reviews don’t look good and apparently it’s a crazy long process and I can’t afford wasting so much time).
Can you define issues?
I’ve owned a HX750i since new and it’s still running strong now, no issues at all.