Alibaba is much better than Amazon about seller verification. Look up, say, "PC power supply". On Amazon, you're lucky if you get the address of the seller and a product image.

Alibaba gives you multiple detailed pictures of the object, including its data plate. You get the full address of the seller, and whether it's the manufacturer or a reseller. There's usually a picture of the factory, info about their annual sales and number of employees, whether that's been verified by a third party, how fast they usually respond to inquries. Sometimes even what production equipment they use. What certifications they have and who does their certifications.

Many of those companies will accept an order for one unit.