Sorry to make it sound easy. I think it is doable and not too tough, but I did click around in loops a few times and then it seemed to work and keep working. No one is stupid for not figuring out random technology that works different in slight ways on different manufacturers etc... Anyway...
In Alexa, if you hit More on the bottom right, then Settings, then Device Settings, do you see "Alexa on This Phone" and also your charger? I think at least your charger is there. What about your "AutoVoice Smart Home Device? That needs to be set up in AutoVoice.
I remember the "sign in to link" being a bit finicky or not exactly explained, but part of the issue I think is that Alexa, the charger, Tasker, Autovoice, are a bunch of things to connect and João is not a 150-person software team (but does a good job fooling everyone). I think the order might not be totally linear for every device. I've seen instructions for YEARS with different hardware and drivers etc, "try installing it three times, it worked for some users." Even though we want such a statement to be nonsense it is still true. The sign in page might not appear right after you click your account. After that, try the below part anyway.
On my "AutoVoice Devices" page in AutoVoice, I see a blank icon, but things seem to work. In "Alexa Smart Home Devices" I see "MyDevice" with various
capabilities like percentage and on/off enabled. I set those up pressing + button.
Try signing in on the top AutoVoice Devices? Then, whatever result, go to the "Alexa Smart Home Devices" and click + then make a device. Do you see that device in the Alexa app's "Device Settings"? In mine, I see Alexa on This Phone, my device added AutoVoice.
If you can see your AutoVoice Smart Home Device, then in an Alexa Routine, you make the Smart Home action go to your named device, and send "On" or "Percentage 0" for example.
Then in Tasker, create a profile, Event, AutoVoice Smart Home, use your Virtual Device and Virtual Action of "Set Percentage".
In the Task the profile triggers, it Performs a Task named "phone %avpercentage"
In the Task list, there is a task named "phone 0"
"phone 0" in your case is a pre-defined task, simply "turn on charger".
You could make "phone 1" turn OFF the charger.
The way you would do that in Tasker is with the AutoVoice action "Trigger Alexa Routine".
So.... when you make the command like above Alexa Routine will be triggered by voice or button or other context, like normal Tasker.
Importantly, if you are interested in other smart devices, you'd be totally set up to add them in after doing the above (without the big device in your living room).
Otherwise, you should be able to set up the above, then uninstall Alexa, and the documentation says it should work still...