Your picture shows that you have the wires in the correct place, BUT,
the version of the PMDX-424 that you purchased is designed to be
powered directly from the AC mains. You should connect 120 VAC,
or actually any AC voltage between 100 VAC to 250 VAC to those
terminals. The safety ground from the mains does not connect to
the PMDX-424 since it is fully isolated and does not have a metal
enclosure.
It appears that the voltage that you connected is only 60 VDC, so
you have not harmed the unit.