ONETAK NEMA 14-50P to 6-15R 6-20R ETL Listed 4 Prong Plug to 3 Prong Receptacle Female Outlet 240V 20 Amp Welder Welding Dryer EV Charger Power Cord Adapter

You just need the right adapters to connect the C14 connector on most PSUs to NEMA 14-50R. Use these two:

https://www.amazon.com/IronBox-Electric-Connector-Power-Cord...

https://www.amazon.com/14-50P-6-15R-Adapter-Adaptor-Charger/...

As long as the PSU has proper overcurrent protection, you could get away with saying it is designed for this. I suspect you meant designed for higher power draw rather than merely designed to be able to be plugged into the receptacle, but your remark was ambiguous.

Usually, the way people do things to get higher power draw is that they have a power distribution unit that provides C14 receptacles and plugs into a high power outlet like this:

https://www.apc.com/us/en/product/APDU9981EU3/apc-rack-pdu-9...

Then they plug multiple power supplies into it. They are actually able to use the full available AC power this way.

A (small) problem with scaling PSUs to the 50A (40A continuous) that NEMA 14-50 provides is that there is no standard IEC connector for it as far as I know. The common C13/C14 connectors are limited to 10A. The highest is C19/C20 for 16A, which is used by the following:

https://seasonic.com/atx3-prime-px-2200/

https://seasonic.com/prime-tx/

If I read the specification sheets correctly, the first one is exclusively for 200-240VAC while the second one will go to 1600W off 120V, which is permitted by NEMA 5-15 as long as it is not a continuous load.

There is not much demand for higher rated PSUs in the ATX form factor most here would want, but companies without brand names appear to make ones that go up to 3.6kW:

https://www.amazon.com/Supply-Bitcoin-Miners-Mining-180-240V...

As for even higher power ratings, there are companies that make them in non-standard form factors if you must have them. Here is one example:

https://www.infineon.com/cms/en/product/promopages/AI-PSU/#1...