Seriously, we don't know. It really is a no-name brand. You've had it for 5 years. We don't know how much wear and tear it's had. We don't know if there are issues with the cores or not all we can tell you is that the number (500W) you gave us is adequate for the number (300W) Nvidia requires for that graphics card and a CPU.
All the rest of this is not in any area we can give you any reassurances. Nor is it probably right that we try and worry you, but experience indicates that power supplies (as most other electronics) have a finite life with a failure rate that may increase as the device gets older.
Try as I may, I have no warm and fuzzy words for you. I think that you spend your money on new components and I would be sad if they are damaged by a bad power supply. But if you can't use your components, I can see that that is also not a good place to be.
Ultimately, the risk is yours.