I'm sorry if it sounded like I want to offend you because I wasn't.No 2000w Server PSU from any reputable manufacturer that I have seen has a 24 pin on it, because server motherboards do the breakdown you see in that connector, so unless you find a way to not feed 166amps into the motherboard connectors which can't handle that, what can happen? You burn the connector, or you fry the chipset, or worst case you fry the CPU (unlikely though). Theres a reason the 24 pin is broken down like that, because different parts of the connector go to different parts of the board, and you don't want to exceed the power capacity of the wiring.
Now, Is there a way to do this? Well yes there sure is, but its complicated, and from your line of questioning beyond your level of electronics expertise. You're not doing it with adapters, you are going to need to bust our the soldiering iron, some capacitors, resistors, etc. Its one of those if you have to ask you probably shouldn't be doing it type of deals.
If you're paying $50 for them they are used, there is no way you're buying new ones for that price unless they are stolen, or cheap junk. They are between $300 and $400.
If you're finding ones with 24 pin connectors on them, then they aren't quality units. I don't care about the Platinum rating, that is efficiency only and has no bearing on quality.
We were not talking about providing 24pin ATX directly from the server PSU. We're talking about providing 12V to Pico PSU -> ATX 24pin. OR one ATX psu -> y-splitter-> four ATX 24pin. And adding to that direct 12V from the server PSU to 4+4 CPU connector. I'm not really sure if it is safe. I know that CPU is similar to GPU in regard to the voltage they use. They both use 0.4-1.5V range. And both have VRM circuits to convert from 12V. Technically, if GPUs work just fine from the separate PSU CPU should also be happy. In that case the power consumption from the Pico PSU should be really low and I can run the mobo from like 120W Pico PSU or four mobos from 400W ATX PSU with Y-splitters.
You see the point?
Now regarding the used PSU. Yes, they are used. Doesn't necessarily mean they are bad. Just replaced because the system they were running in cost >50k USD new and it should be replaced because of the critical load these servers serve.