said by Shootist:
To my knowledge there is no computer that output power to the USB ports when the system is shut down, turned off. Maybe when in sleep mode but not powered completely off.
My ThinkPad X220 does, kind of.
In the BIOS setup, under USB there is an entry called 'Always on USB Charge in Off Mode', and the description says
Enable/Disable charging iPod(R), iPhone(TM) or BlackBerry(R) smartphone during hibernation mode or turned off
[Disabled] Disables charging during hibernation mode or turned off.
[Enable] Enables charging during hibernation mode or turned off.
The on-line help says
Enable Always On USB
When the Enable Always On USB check box is selected, USB power is supplied even when the computer is in standby mode, in hibernation mode, or turned off. When the computer is in hibernation mode or turned off, the Always On USB feature works only when the computer power is supplied through an ac adapter.
Note the last line: must be connected to an external power source to work.
I just tried it for the first time and it was able to initiate charging on 2 of the 3 mobile phones I experimented with. Not too useful IMO, because I always carry a USB power supply and would use that if I have access to AC.