Update from me as well:
Spoiler:
When charging is unreliable (with an accessory cable, even a higher pricey one), try the included cable from the original package, if possible.
Longer version:
I made further tests, including measuring charging voltage and current with a usb-measurement device. The latter is looped in the charging circuit in the following way:
Charger -- USB Cable 1 -- Measurement Device -- USB Cable 2 -- Pixel 8.
For below tests I usually left everything from Charger to USB Cable 2 static and just made the final connect/disconnect between USB Cable 2 and the Pixel.
Setup 1:
- USB Cable 1 was the supplied (out-of-the-box) cable -- in case of my pixel 8 a relatively thin, white usb-c cable.
- USB Cable 2 was of the cable type I have been using most times in the past, like in my first comment above (see https://discuss.grapheneos.org/d/4227-not-charging/10 ). It' s a chinese model, high diameter usb-c cable, which I had bought separately and considered it relatively high quality (USB4 compatible, 40 Gbps, 240 W, has done everything it should until the pixel charging...).
Result 1: Charging was unreliable as described. That is, sometimes not "activated", until some point during a reboot.
(Actually it's funny to measure and observe live when the pixel lowers the resistance and draws current and when it goes into higher resistance again. This goes up and down at certain points during the boot process, until it finally "settles" on the desired charging current.)
Then I swapped Cables now to
Setup 2:
- USB Cable 1: the high diameter, extra cable
- USB Cable 2: the supplied (out-of-the-box), thin cable
Result 2:
From ca. 20 connections of USB Cable, all of them worked without flaw at the first attempt.
Conclusion:
Using some extra accessory cable can be an extra source of errors - even if you consider it to be of proper quality. In my case, I suspect that electrical imperfections make my "high diameter" cable unsuitable when it's used for the final connection between usb measurement device (or charger) and the pixel. Maybe that 240W-certified cable is just too "big" for my charger/Pixel 8-Kombo, which regularly just draws ca. 7 W.
Speculation: Maybe there is some parasitic capacity that disturbs the circuit in such a way, that the charging can't be unlocked at first, until a reboot neutralises that disturbance.
If some electrical expert with more in-depth knowledge of the Pixel (8) charging circuit can provide a more elaborate theory, feel free. I'd be happy to learn.
For everyone just interested in reliable charging: It might be the solution to test more cables, especially the original cable from out-of-the box if available.
TL;DR
Bimmy made more measurements and now concludes that the cable probably was the problem. Out-of-the-box cable seems to be the solution.