A simple remix to create a gridfinity block for USB chargers.  It has the slots for US-style power plugs (NEMA 5-15P).

If you want it longer or shorter, the OpenSCAD file is here:
https://github.com/afaucher/gridfinity-charger-bin/tree/master

The remix takes an existing gridfinity OpenSCAD library and adds slots.  Nothing crazy.