Your unit is powered by two replaceable power supply modules (either AC or DC). Your unit needs only one power supply module to work, but it can house two of them. The second power supply provides redundancy.
The power supply modules are hot-swappable, which means that you do not have to turn off your system to replace one of them. There is no need to disassemble the unit to replace such a power supply.
Ensure that you replace the defective power supply with a new one of the same type (AC or DC).