Identification: what type of connector does the pictured socket take?
Thats a terminal block header probably the same one shown below:

Source: https://www.digikey.com/product-detail/en/on-shore-technology-inc/OSTOQ045451/ED2830-ND/1588283

The terminal block plug can be found below


Source: https://www.digikey.com/product-detail/en/on-shore-technology-inc/OSTTS04515A/ED2863-ND/1588621