An uninterruptible power supply, UPS, system in communication with a recovered power bus, the UPS system comprising: a plurality of UPS modules (102(a)-(e)), one or more of the UPS modules (102(a)-(d)) usable to provide stranded power to the recovered power bus; and associated with each said UPS module (102(a)-(d)) which is usable to provide stranded power to the recovered power bus: a static transfer switch; and a load; each of the one or more UPS modules (102(a)-(d)) having a first AC power output coupled to a first AC power input of the associated static transfer switch, a third AC power output associated with said static transfer switch being coupled to the load, and a second AC power input of said static transfer switch being coupled to the recovered power bus; characterised in that the UPS system further comprises, associated with each said UPS module (102(a)-(d)) which is usable to provide stranded power to the recovered power bus, an AC/AC converter that is configured to receive the first AC power output from the associated UPS module (102(a)-(d)) at an AC input thereof, and that is configured to generate a second AC power output at an AC output thereof, which is configured to be applied to the recovered power bus; and when any of the one or more of the UPS modules (102(a)-(d)) is used to provide stranded power to the recovered power bus, its associated said AC/AC converter is configured to provide, at its associated said AC power output, the second AC power output, the second AC power out configured to be synchronized with other ones of the second power outputs being provided to the recovered power bus by each of the other said AC/AC converters that are providing AC power to the recovered power bus, so that the second AC power outputs of all of the AC/AC converters that are being provided to the recovered power bus have at least one of the same voltage, the same frequency, or the same phase. a plurality of UPS modules (102(a)-(e)), one or more of the UPS modules (102(a)-(d)) usable to provide stranded power to the recovered power bus; and associated with each said UPS module (102(a)-(d)) which is usable to provide stranded power to the recovered power bus: a static transfer switch; and a load; each of the one or more UPS modules (102(a)-(d)) having a first AC power output coupled to a first AC power input of the associated static transfer switch, a third AC power output associated with said static transfer switch being coupled to the load, and a second AC power input of said static transfer switch being coupled to the recovered power bus; characterised in that the UPS system further comprises, associated with each said UPS module (102(a)-(d)) which is usable to provide stranded power to the recovered power bus, an AC/AC converter that is configured to receive the first AC power output from the associated UPS module (102(a)-(d)) at an AC input thereof, and that is configured to generate a second AC power output at an AC output thereof, which is configured to be applied to the recovered power bus; and when any of the one or more of the UPS modules (102(a)-(d)) is used to provide stranded power to the recovered power bus, its associated said AC/AC converter is configured to provide, at its associated said AC power output, the second AC power output, the second AC power out configured to be synchronized with other ones of the second power outputs being provided to the recovered power bus by each of the other said AC/AC converters that are providing AC power to the recovered power bus, so that the second AC power outputs of all of the AC/AC converters that are being provided to the recovered power bus have at least one of the same voltage, the same frequency, or the same phase.