Mac USB ports provide the identical amount of power as PC USB ports. Should be no different. The Vita would be off, so it's not like it would fail because the Mac can't mount the device. Maybe I wasn't following the discussion very well. I was just trying to point out that, technically speaking, the Vita is always charging via USB. The AC adapter literally has a USB port on it. So the only difference is how much power a specific USB port can provide. If it's enough, like a wall adapter, the Vita can be powered up. If it is no enough, like a Mac or PC port, it needs to be powered down.