USB charge current?

The device being charged is my 10" tablet, which is “off”.

The charger is a 2A power pack with one of those power meter gizmos connected.

The charging lead is a short USB to micro USB lead. Given that it is intended for charging my sphygmomanometer, I doubt that it is fully wired.

Now, the odd thing is that if I connect the lead to the tablet and then plug it in to the power pack (via the inline meter), it begins charging at the default USB standard of 0.05A.

However, if I first connect the lead to the power pack (via meter) and then to the tablet, it charges at a much better 0.80A.

It seems strange that the same equipment, differing only in order of connection, behaves in such different ways. As, well, 0.05A won’t get you charged in a hurry. In fact, I’d imagine the tablet, when on, drains the battery faster!

at a fairly random guess, plugging the lead in is detected by the tablet end, which tries to negotiate a rate and gives up. If the lead is already connected to the meter, the negotiation succeeds.

0.05A? A tenth of “standard USB 1.1/2.0”?

And: whenever negotiation for higher charging power happens, not only the amps change, the volts can change, too. Always frightened me a bit, seeing all those possibly buggy implementations before my inner eye…