This product is either discontinued or we cannot get that from suppliers.
Cisco C4KX-PWR-750AC-R Catalyst 4500x 750w Ac Front To Back, Power Module, Input Voltage 110 V AC, 220 V AC, Compatibility Cisco Catalyst 4500-X Switches Series.
CISCO C4KX-PWR-750AC-R Catalyst 4500x 750w Ac Front To Back Cooling Power Supply.