cross-posted from: https://infosec.pub/post/51092505
I have a 3-pin Dell PSU spec’d as 19.5v 3.34A and DMM measures at 20v unloaded. The power reqs on the HP laptop are 19.5v 3.33A. AFAICT, that’s a match. Even the 3-pin barrel connector geometry matches. So what’s the problem?
The center pin is a “smart pin” aka “data pin”, as I came to learn. According to @over_clox@lemmy.world, this PIN basically passes brand info so HP can reject non-HP PSUs. But according to this article, the data pin is used to “regulate” the voltage – which I take to mean it negotiates the voltage for transmission as USB-PD does. If it’s merely negotiating power reqs, then the Dell should work.
It’s possible both sources are correct… perhaps HP has its own proprietary way of negotiating voltage and Dell has theirs.
Someone even claims that the data channel is used to communicate temp info so a PSU does not overheat. If that’s true, then perhaps it was a good design (noting that the USB-PD standard did not emerge yet).
But is it true about the communication? Considering there are hacks with a resistor or something to satisfy the data channel, it’s hard to believe that the communication is that sophisticated.
This page advises HP owners to always buy HP-branded PSUs. But it’s unclear if that’s just overly safe nonsense.
ahhh, I miss the days of analog power … these days almost every charger has power negotiation using proprietary protocols. Some more popular than others.
Look it up on youtube, there’s a bunch of people that dedicate a shit ton of time to reverse engineer the negotiation phase with an oscilloscope. That’s why you can now buy charging modules that convert analog to digital.
I don’t do youtube, which has descended into a shitshow of Google blocking both Tor and also killing off invideous instances. But I have seen some hacker pages with pics of this hacking. In any case, it’s a mess. It used to be that only dumb consumers got burnt (as they would mismatch voltages). But now smart consumers can get burnt too because even when the levels are good the nannying protectionism cock-blocks.