Xbox Series X parts?

Hi everyone! My friend had his Series X for a while now (I don’t see any category created for this forum) and it suddenly started crashing for him (I suppose he means dying, not crash to dashboard) and then it would not turn on. I’m wondering whether it is a hard drive issue or power supply issue. He has since ordered a new one because of the warranty. Regardless, where do people get their parts for the various consoles? Ebay seems too risky as you might not always get top quality items.