Why two power ports on a budget laptop??

[moonwalkers]

You're right on both of the points above.  If the battery charging current (or the max. current available from the charger) is greater than the current required by the computer, the battery may be charged.  Otherwise, the battery will be drained to compensate the difference.  The underrating of the charger outputs and overestimation of the system power consumption is what actually makes such "charger overclocking" physically possible.

No offense, but frankly speaking you're not making much sense here - going back to my pretty tired by now example of R50 with a 30W PSU, it matters very little whether the PSU is capable of outputing 36W when it's rated for 30W if the machine expects 72W.

What does matter, however, is that even the simplest PSUs like the one I have in my Soviet EleKtronika MK-52 programmable calculator from the early 80s usually have voltage regulating and current limiting circuits that protect both the device and the PSU itself by providing stable voltage up until certain load, at which point the voltage starts to drop. And when voltage drops the device can no longer draw any more power from the PSU and will have to supplement it from a battery, if one is available, regardless of the excess tolerance on the PSU.

The trouble with the PineBook Pro is that the battery charger IC is configured to think that the computer needs no power to operate, so the entire input power from the charger is capped at the max. battery charging power, while it could go higher.  All of that goes back to the above-described behavior.

That's one way to put it.

However, I've switched from the factory-installed Debian to Manjaro ARM on my PineBook Pro, and it seems that one of the charging issues was caused by some weirdness inside the Debian's Rockchip-provided Linux kernel, which caused much higher power consumption.  The laptop is actually now able to stay away from discharging the battery while being subjected to pretty much the same load as it was the case with the factory-installed Debian, which used to cause the battery to become completely drained in a few hours, despite the laptop being connected to the 5 V, 3 A charger.

I used the Rockchip-provided kernel only for as long as it took me to prepare a microSD card with (nearly) stock Debian using the unofficial "installer" script by danielt@, which is barely a couple hours after I opened the DHL package. And even then, soon afterwards and all through now I've been using the Manjaro kernel with my Debian installation. So whatever charging weirdness I've been experiencing is definitely _not_ due to Rockchip kernel. I've been keeping all my firmware blobs up-to-date, BTW.

However, I expect the laptop not to discharge its battery down to 0% and turn itself off while being connected to the factory-supplied charger.  Such behavior is simply not acceptable; however, that's exactly what I've experienced with some light usage, i.e., low CPU load, WiFi off, etc.

100% with you - even if the stock PSU doesn't support full load without discharging, the design should at least allow for such option to exist as an aftermarket purchase.

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I think the point is that while barrel jacks are immensely reliable they're not consumer friendly as they fail the principle of least surprise. Pick an arbitrary barrel jack. What voltage and current does it supply? Will it fit in your device? Will it be safe to plug in? No idea to all of the above.

USB-C on the other hand I know it will plug into my USB C device and I know it'll power it without causing any damage. It might not charge my laptop, I need a special charger for that but there are keywords to search for. The worst case is it doesn't charge, not 'it explodes'. It's also pleasing that most 20V barrel jack laptops can be charged off a PD supply with a simple trigger adapter (the other way around is a lot harder!). That said I tried a new smaller USB PD charger today that doesn't want to stick in 20V mode without re-negotiating every few seconds so there's room for improvement on the surprise front.

Not to rain on anyone's parade--I gladly take advantage of the USB charging PBP allows--but only to explain why USB charging is neither the panacea nor the silver bullet of charging it's been treated as....

There is a difference between simplicity and POLA (principle of least astonishment), and traditional non-USB power supplies are definitely simpler.

And even when it comes to POLA... When I grab a barrel plug PSU it has markings for the voltage, current, and polarity it provides. I can't remember seeing even one that doesn't. And virtually all devices that use barrel plug PSUs have markings next to the socket that tell you the voltage and polarity they need, except for maybe the hobbyist devices and the likes that don't go through proper mass-market certifications. Make sure the voltage and polarity match and you can actually plug the cord without it being loose - and the worst case scenario the PSU doesn't provide enough current, the same exact situation as with your described USB C deal.

If you know how much current your device needs you can tell right away whether any random PSU will be able to provide that - it's written on the PSU itself. That said, while barrel plug PSUs come with the cable integrated, when you pick up any random USB C cable you cannot be sure whether it will let you use the full power the available PSU can provide, and as far as I'm concerned that goes right against the very POLA you brought up, leaving you wondering why your clever 100W USB PD PSU doesn't charge your shiny new USB PD laptop--a situation I've ran into myself a couple of times with the employer-provided machines.