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That varies dramatically depending on the revision of the USB used on the port.
Yes, a USB port can supply a small amount of power for attached devices.
Usually you plug something in to the USB port to either give it power, or charge its batteries.
A COM port can not be converted to a USB port just by using software. The signal types, levels, protocol, connector type all are different.
You can charge your Touch by connecting it to any computer's USB port, by using a plug-in USB power supply, or by using some form of USB battery pack. I don't know if any of these fit your definition of "without using a charger".
Whether or not a USB desk fan will work on an HDTV's USB port depends on the purpose of the port. However, in most cases, it will likely power the fan.
Assuming your using a USB port to power your device, the answer is 2.5 Watts. A maximum of 500mA at 5V can be drawn from a Usb port. Power = Current * Voltage, which is 2.5 Watts by 0.5 Amps giving you a power output of 2.5 Watts http://en.wikipedia.org/wiki/USB#Power http://en.wikipedia.org/wiki/Power_(physics)#Average_electrical_power_for_AC
You can have a USB Serial (COM) port and you can connect PCs together using Serial (COM) port.
COM port is used to configure a router but you can also get a COM port to USB port adapter which can configure a router using a USB port.
uSE THE usb TO ATTACH COMPUTER. POWER PORT IS ALSO USB PORT. SPECIAL SIZE
Try plugging it into another usb port. The particular port may not have enough power.
Using active hubs you can connect 127 devices to each USB port.