Not sure about the ICOM specifically, but in general, the specifications for a USB 1.0 and 2.0 standard downstream port, delivers up to 500 mA or 0.5A. Also, with a USB 3.0, it can provide up to 900mA or 0.9A, which translates into 4.5 watts. These power output specifications are a rating based on the 5 volts from each standard output. I use my PC usb port to power a LED desk lamp in lieu of the original AA cells it originally came with.
73' de Dave - W5BU