Now here’s a question I don’t want to answer empirically:
what happens if/when I plug my HP laptop charger into my L5?
The charger has a 5V output rated at 3.0A and 15W. (Amongst others. There is, for instance, also a 20.0V output rated at 3.25A and 65W.)
I think it should work fine. But I am not sure enough to just have a go.
If the voltage matches, you should be fine.
I think the charger adapts the voltage automatically. It mentions 5V, 9V, 12V, 15V and 20V.
If it is able to match the voltage it should be fine. I use one with variable voltage outputs and I haven’t had any problems
I’ve used my laptop charger. 65 Watt also has a bunch of different outputs. The 5V option is 2A. Didn’t seem to cause any damage.
Thanks for the replies. I think I know enough now to give it a try.
The voltage should work by itself, as should the wattage (if that is a proper word in English), and the amperage is determined by the phone, I would guess.
Quick fun fact: when I plugged the L5 into my Surface tablet I got all kinds off warnings: the Surface could not deliver enough power to support the phone. It’s quite a beast, our L5. 
Librem 5 only uses 5V. 3A is max, so if the charger does 3A at 5V, you’re all set.
A laptop charger can fry a Librem 5, but only if it’s terribly broken and behaves out of spec - but then many other devices won’t stand a chance against it either
So did you try it yet? If so, did it fry your L5? 
So this is a Surface from the last few years so that it even has a USB-C port?
Might be fun to have output from
cat /sys/class/power_supply/tps6598x-source-psy-0-003f/uevent
to see whether power negotiation failed and/or what it resulted in.
I have successfully used my Apple usbc laptop charger with no problems. I’d only be concerned if the charger was a cheap/generic brand, even if it would likely work fine.
No, not yet. It was night time here. Will give it a go today. Probably.
(Still somewhat apprehensive.)
I used a usb-c-to-usb-2 cable.
And I am not sure whether I want to repeat the experiment.
If you are saying that the Surface that you have only has a USB-A 3.x port then likely it doesn’t explicitly support delivering power at all as such … and will only negotiate 500 mA, which is barely enough to charge the Librem 5 while operating the Librem 5 (and what the USB port could deliver to any USB peripheral).
Assuming that the Surface runs Microsoft Windows then it probably can’t readily have the uuu software either.
So, as far as I can see, connecting the Librem 5 to the Surface serves very little purpose anyway. (A more modern Surface with an actual USB-C port might be a little more interesting.)
It’s not even a usb-3, it’s a 2 (I did an edit). But admittedly it is an older Surface 3 pro. There is definitely no usb-c port.
I did not have great expectations about the connection anyway. Microsoft now promotes coupling an Android phone to their Surfaces. When I connect my Windows Phone nothing happens. I think it might function as a thumb drive at best - and Windows hardly excels when it comes to handling those (it’s an error fest!).
Meanwhile from the charger front: it seems to work fine. No smoke just yet. Phone stays pretty cool. Nice! Now I only need to carry one charger.