also a few things to note:
(1) current (and in the case where voltage is constant, this also includes power aka watts) is supplied on demand, where the peripheral being powered or charged is making the demands. So electrically speaking, a device that "demands" 7 watts of power won't care if the power supply is capable[i/] of producing 12 watts. or 20. or 500. The supply will only be able to provide what the accessory demands. A power supply with a much larger than necessary capacity is absolutely NO risk to anyone. This is a common misconception, I run into people from time to time that think you can't safely plug a 20 watt accessory into a 50 watt power supply "because the power supply is too big and will fry the accessory". That's not how electricity works.
(2) if the accessory demands more power than the power supply can safely provide, there are several possible outcomes:
A- the power supply may detect the excessive demand and just plain SHUT OFF completely (best option for a good "smart" supply)
B- the power supply may "sag" and lower the output voltage. Power supplies have a limited output power, in watts, and watts is volts x amps, so if the accessory is supplying too many amps (at the designed volts) then all the supply can do is shut off (A) or drop the volts so volts x amps is at or below the supply's ability to deliver the watts. "intelligent" accessories will notice the sag, stop charging, and display a warning on their display (if they have one) to indicate there is a problem with the supply.
C- the power supply may blindly continue to provide as much power as it can (often with some amount of sag) but since they are handing more than their rated power, they will overheat, which may trigger them to automatically shut down, smoke and die, or catch fire. This doesn't usually damage the accessory [i]electrically, but the fire may be a bigger concern.
So if the power supply is dumb AND the accessory is dumb, it may result in dead, smoking, or flammable power supplies.
Anytime a peripheral (like a phone left on charge) is overheating or catching on fire is ENTIRELY a problem with the accessory, not the power supply. All accessories should be expected to keep an eye on voltage and current levels and cease their demand on the power supply if they notice a problem.
None of this changes when switching from wired to contactless charging.
Somewhat recently USB standards were updated to allow power supplies to notify accessories (cheaply) how much power they could supply, which allowed accessories to adjust their demands based on what the power supply claimed to support. Many newer devices (iPhones for example) will refuse to charge at all (make no demand) if plugged into a supply that doesn't provide this information, "because they don't know how much power they can safely draw". You will see an error message on your iPhone when attaching to a "dumb charger". This does not prevent a dumb accessory from still trying to demand more than the power supply can provide, and all of the above rules will always remain in effect.
This also does not stop scrupulous manufacturers from rigging their power supplies to indicate they can provide more power than they are able to safely produce on a continuous basis. This is generally where we see charger fires nowadays. Cheap chargers from China that are rated on the package and over the USB to supply 10 watts (2 amps at 5 volts) but that can only supply, for example, 5 watts continuous, or 7 watts for a short time (with a sag down to 4.8 volts) or 10 watts with significant sag (4.2 volts?) for a few minutes, before overheating and possibly igniting.
