When a UPS (Uninterruptible Power Supply) is turned off and acting as a pass-through for the AC power, it is not providing any active power backup or conditioning. In this mode, the UPS is essentially bypassed, and the connected devices receive power directly from the main power source.
In this state, the UPS doesn't have any impact on the power load, and its capacity is not utilized. Therefore, the UPS can handle the entire power load it is rated for, which in your case is 1440 watts. It acts as if it is not even there in the circuit, so you can use the full capacity of your UPS while it's turned off and acting as a pass-through.
Just be aware that when the UPS is turned off and acting as a pass-through, there won't be any protection or backup power provided in case of a power outage or voltage fluctuations. It's important to use the UPS in its intended mode when you need the power backup and protection features.