Question PSU "problem"

May 12, 2019
Hi guys, i could use some help from you.

So..long story short...
Recently my friend and i bought the same graphic card, ASUS RX570 expedition, from the same guy (used, three months old).
We also have exactly the same hardware( we are good friends ) except for the power supply. He bought brand new LC Power 550w and mine was from the same brand 560W GP3 but 7 years old. I know you all hate LC POWER but i didnt had any problems for this many years until now.

So, shortly after i was getting these black screens, rarely and randomly and only when i played some games. This didnt happened with my old radeon 7850. My friend don't have these problems when he plays the same games so i suspected that my power supply is bad or insufficient. It was already very old so i decided to buy new one. I bought ANTEC NeoEco NE650C and everything is working fine for the moment although i didnt have time to test it in games but i did some basic testing with my multimeter and these are the readings:

Cold test: 11,93v / 3.34v / 5.25v. Mounted and idle: 12.26v, under load 12.07v ( i didn't tested 3.3v and 5v in my pc, sorry)

Mounted and idle: 11,90v, under load 11.85v

So my questions are...

Can the PSU be bad even if voltages are in safe limits?
Did i made mistake by buying the ANTEC? I guess then, that my GPU is bad...
What about the voltages on ANTEC? Should thay be slightly over 12v or is this normal?

Sorry for the long post and thank you...