Apple Watch Magnetic charging cable (connected via USB-C)

Because it is basically a cable, just like the cable for your iPhone, it CARRIES power, it does not PRODUCE power. If you connect the device you pictured to the 20watt power adapter I posted the puck/cable will CARRY 20w to the puck at the end. If you connect it to a MacBook Pro power adapter it will CARRY 85w to the puck. But the Watches power management circuitry controls all charging and it will only ACCEPT 12w.

A cable can only carry power, they cannot produce it. The power adapter in your scenario produces it. You question is tantamount to asking how many watts an extension cord produces.

jacob__k wrote:

Ok, that's fine. Does the size of a wireless charging coil affect its charging rate/speed? For instance, does the size of the wireless coil in the MagSafe wireless charging cable (for iPhones) and the Apple Watch Magnetic charging cable (via USB-C) affect each of their charging rates/speeds?

The Apple Watch controls how fast it draws power from the puck. As long as the puck meets the Apple Watch charging standards, then at most the Apple Watch will draw 12 watts. ONLY if the puck does not have 12 watts to offer, will the Apple Watch draw less than its maximum, until the Apple Watch is fully charged, then at most the Apple Watch will trickle charge to maintain the 100% battery while on the charger.

The charging brick, the charging cable, and the charging puck DO NOT control the speed at which the Apple Watch charges. The Apple Watch is in control of that at all times.

The Apple USB-C charging brick can output up to 20watts, HOWEVER, the Apple Watch will only use 12watts of that.

Get a USB-C Power monitor

https://www.amazon.com/usb-power-monitor/s?k=usb+power+monitor

and measure it for yourself.

Watts is voltage times current. You do not control voltage, so the current (amps) is what varies. The Apple Watch only sips 12 watts no matter how much is available.

Using a power meter will report a higher wattage, but only because there is some power inefficiencies and losses in the wire and generating a magnetic field. There will be heat losses as well (another inefficiency).

Put another way, I can put a 100 gallon gas tank on my lawnmower, but it is still going to use the same amount of gas to cut my lawn as it did with the 1 gallon gas tank. It is not how much gas is available, it is how fast the lawnmower consumes it.

The same is true for the Apple Watch charging cable. It is basically going to draw the amount of power accepted by the Apple Watch, plus some extra for inefficiencies.

None, it can't produce any power in volts, watts or amps. Click on the link I posted and that power adapter can produce power, 20watts in fact, to the cable you posted.

Try Apple support

0 watts. It cannot produce any watts.

The cable itself, with the magnetic puck on one end and the connector on the other cannot product any power output. Does that answer your question?

Essentially any Apple power source and cable that fit into the connectors at either end are compatible and safe to use. For moire info, see:

When to charge your iPhone or iPad - Apple Community

(which also applies to the watch - see footnote.)