This is not a US electrical outlet, but it's one I've recently become aware of, which folks might find interesting:

Our next data center, for the HPC portion, may end up getting 480 VAC to the rack, with each outlet getting 277 VAC (one phase plus neutral and ground). If you order a generic Dell server, you'll find they now have power supply options for 277VAC.

What's the outlet? The D-Grid 400 (SDG 400). So, there's another outlet to add to the list!