Quote:
Originally Posted by Richwood
Quoth;
Also older or cheap USB power/data cables can limit charging current too. Current heavy duty USB Micro or USB C charging cables can be rated for up to 3A at 5V nominal and some USB C cables for 5 A at 20V. Older cables may only be good for 500mA at 5V per what I have read.
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Older cables unless total rubbish are OK for 2A. It's just copper wire and usually not very long. Ohms law rather than magic applies.
The charger/port "signals" what is possible and the gadget decides what to take. So if Gadget is 2A and the host port is 0.5A (500mA), the gadget charges fine at 500mA. If the gadget software/hardware can't make sense of the state of the D wires it takes 100mA or 500mA.
The only major difference with a power plug vs a USB connected charger, is that a charger with a power plug must be able to do AT LEAST the full current as there is no mechanism to tell the gadget what to take.
Devices will always take less than the stated current and voltage as those are absolute maximums.
USB C is more complicated, but the higher voltage modes are so to avoid having copper wire any heavier than USB - A port hosts. There are all kinds of compatibility issues and also quality issues on USB C chargers as the charger is no longer a fixed signal, 5V only and limited current.