The TC-500P8A power supply is a redundant Passive PFC EPS 12V 500 watt server/workstation power supply consisting of two separate units. It main outputs consist of the 24, 20, 8, 4pins plugs. During normal operation, both are used in equal measure; if one of them fails, the other takes over the whole load. One special feature is that the power cables can feed both sub-units: if the power from one line goes out, both sub-units get their juice through the other line. I-Star patented this design under the name of "True DUAL AC Input."If a failure occurs, the failure LED of the affected sub-unit lights up and a buzzer goes off; there is a button to deactivate the buzzer. Fixing the problem is easy: just turn off the unit in question, unlock and remove it, then put in a new unit and turn it on. While that is going on, the system continues to receive power from the other unit.