Hmm, I don’t have direct experience with ThinkServers, but what I see on eBay looks like standard ATX hardware… which is not really what you want in a server.
The Dell motherboard has dual CPU sockets and 8 RAM slots. The PSUs are not the common ATX desktop format because there are 2 of them and they are hot swappable. This is basically a rack server repacked into a desktop tower case, not an ATX desktop with a server CPU socket.