[PLUG] Powered USB-A hub - LSUSB MaxPower

[MC_Sequoia]

I was a bit skeptical about this MaxPower rating for a couple of reasons so I did some digging and I think I found some evidence to support my 
skepticism. 

Why is MaxPower given in Amps and not Watts? 

I suspect it's because MaxPOower refers to the usb bus and not the usb device connected to it. 

Here's 2 data points to support that theory.

1. "USB device configuration descriptor expresses bus power electrical current requirement in field bMaxPower." 

"usbutils 008 lsusb misreports MaxPower for SuperSpeed devices.  For example, lsusb -v outputs 'MaxPower 500mA' when a device is connected on 
High Speed bus, but 'MaxPower 224mA' when connected on SuperSpeed bus. usbfs devices holds correct 'MxPwr=896mA'."

Reference - https://www.spinics.net/lists/linux-usb/msg124590.html

SuperSpeed and HighSpeed refer to different USB bus standards. 

"SuperSpeed USB is ten times faster than USB 2.0 (also called HighSpeed USB) and increases the power output from about 100 milliamps to 900 milliamps."

Reference - https://www.techtarget.com/searchwindowsserver/definition/USB-30-SuperSpeed-USB

2. Electrical devices are rated by watts that you can find listed on them and circuit breakers are rated in amps. Why?

Because the amp rating is about capacity/output. For example, my rechargeable battery charger says:
 "Output - 220 mA - AA x 2
            80 mA - AAA x 2

3. "As with earlier versions of USB, USB 3.0 provides power at 5 volts nominal. The available current for low-power (one unit load) SuperSpeed devices is 150 mA, an increase from the 100 mA defined in USB 2.0. For high-power SuperSpeed devices, the limit is six unit loads or 900 mA (4.5 W)—almost twice USB 2.0's 500 mA.[12]: section 9.2.5.1 Power Budgeting 

USB 3.0 ports may implement other USB specifications for increased power, including the USB Battery Charging Specification for up to 1.5 A or 7.5 W, or, in the case of USB 3.1, the USB Power Delivery Specification for charging the host device up to 100 W.[14]"

Reference - https://en.wikipedia.org/wiki/USB_3.0

So, in conclusion I think the "MaxPower" data point provided by lsusb command is about the bus electrical output capacity that the device is connected to and not about the device itself that's connected to the usb bus.

This might not affect your buying decision, but I think it's worth having correct information and understanding what you're working with.