I have a T450 that according to the specs has three USB ports.

One of those ports is Always On USB port, so even if you turn off the computer, but the laptop charger is connected, this port will be working, so that you can for example charge your mobile phone and other devices. That is port no. 5 on the image below.

ThinkPad T450

So theoretically, when my laptop is turned off but still plugged:

  • devices connected to port 2 (normal USB) should not be charging
  • devices connected to port 5 (always on USB) should be charging

In practice, this is not the case, and it's very surprising:

  • my Sony Xperia smartphone behaves as expected: charges on port 5, does not charge on port 2 (and does not charge on the port on the right hand side)
  • however, my Lenovo tablet behaves exactly the other way around! Charges on port 2, does not charge on port 5 (and charges on the port on the right hand side)

How could this could possibly be the case?


This behavior is very possible when the two ports have different "charging signatures", while the two connected devices have different cohesion to charging signatures.

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