The G650 can use one or two 655A power supplies that can have both AC and DC input power present. Either power supply can provide all the power needed by the G650. When there are two power supplies, they share the power load. One power supply can operate on AC power and the other on DC power. But, if AC power is available, the system always uses AC power. The 655A power supply is the only power supply supported in the G650 and not backward compatible to other carrier types.