Several customers from the U.S. let me know they were surprised not to find a U.S. adapter included with the power supply. They're right. Sorry, I thought you all had adapters like this one in stock.
https://amazon.com/Unidapt-Europe-Quality-Adapter-Converter/dp/B077W89DK1/
For US customers, I did try to buy the 709-NGE12U15-P1J from Mouser, which has the right plug for you. But I'm not allowed to as a French customer!!! I can only buy the 709-NGE12I15-P1J...Are the US worried about technology transfer? :D :D
Otherwise, in Europe, I can buy the MEAN WELL AC PLUG-US4, which is an interchangeable plug that can replace the one you received. I have a few in stock, but I can no longer send small economy packages to the US. So, since shipping via FedEx or UPS would cost with 3 invoices for the socket,
I suggest you try to get it directly. I will refund your fees via PayPal. In the US, you can order it from Mouser, for example, by searching for 709-ACPLUG-US4 (1-2$ + shipping).
Now, I think I'll try to include the AC PLUG-US4 directly in packages sent to the US.
Thanks again !