Vlada011
Is it 4 years and few months long time for one PSU?
How long I should stay on EVGA 1200 P2 before I replace him. 5-6-7 years?
When I say he worked 4 years, that mean 4 years, she didn't sleep over night.
In rear situations on few hours.
I know you asked this a while ago, but it's still a worthwhile question that should have an answer.
One of my first power supplies was a SilverStone, which lasted 8+ years before I decided to swap it out. I used it in 2 or 3 different builds and had no issues. It probably still works fine today, if I test it.
My current 1600 T2 is still working fine after medium work loads over the last 4 years. It still has plenty of juice left in it. That could change overnight, but you can't assume that the product will fail without warning, otherwise none of us would ever buy electronics.
Most power supplies are built extremely well because they have to be. Many national and international regulations require various components to be within specific ranges, have certain tolerances, and other specs that force them to be built that way. Higher efficiency ratings (i.e. Gold, Platinum, Titanium) also require higher quality components and better electrical designs to ensure reliability and efficiency. No, that doesn't mean you can assume that a Platinum is built better than some Gold units, but it takes a fair amount of work to get it rated to Platinum in the first place. This is one of the reasons that many power supplies have anywhere from 5 to 10 years of warranty. Remember, brands aren't going out of their way to offer warranties that assume a product will fail multiple times during the length of its warranty. There's a reason they expect them to last at least that long.
We are in a golden age (pun not intended) of power supplies right now in terms of choices among many solid, well-built, and affordable power supplies compared to the market even 10 years ago. Many good brands exist now, nearly all mid- to high-end power supplies have some level of Japanese capacitors, and even mid- to low-end power supply lines have efficient designs with low ripple and noise.
The only real known issue with age is that the power supply will likely become less efficient as it ages. The degree to which it will lose efficiency will depend on the specific unit. With that said, that doesn't mean the power supply is headed towards failure. Just like a car will lose some gas mileage over its lifespan, it doesn't mean you run out to replace it if it's running fine otherwise.
I wouldn't replace your power supply anytime soon. Unless you have an issue, or you decide to build another system, there's no real benefit to trying to guess when the unit might fail. After all, you could just end up replacing it with a power supply that does have problems, which will require an RMA. Otherwise, the PSU is expected to last at least another 5-6 years. That doesn't mean it will, of course, but there's also no reason to assume it won't.