For USB 2.0 devices this had the benefit of increasing power to a device to the max of what USB 3.x allows. What the USB groups came up with was the USB-BC standard for providing power to devices even though they might not he making a data connection connection to the host. To this end it became customary to allow 100 mA or 500 mA on systems are were "asleep" to allow keyboard wakeup, or all too often run novelty Christmas lights. This was being used for more than it's intended purpose of providing power to parallel port adapters and the like. Being replaced by USB 3.x and USB-PD.įrom the beginning of USB people discovered that was trivial to get 5 V of power from USB ports by just connecting to the V+ and GND.
USB-BC is increasingly becoming a redundant a meaningless standard. The TLDR on this is that sometime in the last 10 years the minimum spec on powered USB-A ports became 1.5 A, and maximum became 3 A, but 2.4 A in practice.
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