All sound generic tbh.
Go for new if you can.
If you know your specs, like CPU and GPU in particular - that will help. Knowing which graphics card is the most important thing.
Unfortunately 500W means little really. Especially when it comes to GPU's since they are the single most taxing/heavy draw component. A psu may deliver 500W in total across the 12v, 5V, and 3V spectrum. But it doesn't mean it can poer EVERYTHING.
As I mentioned above - as long as as you aren't going anywhere near the "maximum' potential, you can get away with a generic PSU.
But ageneric "500W" realistically may only be capable of 400W at full load total across all 12v, 5W, 3V rails. (A rail is basically the separation of voltage usage)
For Graphics cards it comes down to to how much Amperage the 12v rail (section) can deliver. For example if a video card needs 24Amps on the 12V rail (section) to run and the PSU can only only deliver 16Amps on the 12V rail -then that's trouble in the making. Avoid at all cost.
The card may not run, it will cause PC crashes, or at worse blow the entire PC apart if the PSU is pushed to far.
I can understand you're after the cheapest possible unit. We are simply trying to explain how potentially damaging using the wrong and graphics card can be.