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.
So in the context of copious dumb users plugging in anything that fits the socket, the data PIN may¹ have prevented a lot of damage while at the same time enabled HP to rack in lots of money on replacement OEM proprietary PSUs. Indeed I have seen on many occasians clueless plebs at the street market selling 2nd-hand appliances and quickly trying barrels from a pile of tangled PSUs until one fits, then trying to include that with the device they are selling without looking at voltage or anything. It’s common and I’m sure lots of gear gets fried because the general population is just not smart enough.
I know how to match voltage, polarity, and current demands. And I got stung by the nannying to protect me from myself. Spent a lot of time disassembling a laptop, trying different RAM sticks, removing wifi cards and other components as I was baffled about what this fucking blicking LED means when it is not blinking in any way to convey an error code. Removed the CR2032 battery to reset the CMOS. Wondered if my slower than spec DDR3 RAM was causing this, so I went to the trouble of tracking down a RAM stick the precisely matched the specs. Still just got a steady non-stop blink, which the manual falsely states means it’s in sleep mode. So I was ready to conclude that the laptop was trapped in sleep mode and irreparably hosed. Perhaps I would have tossed a working laptop.
Whether it is a good design to protect from incorrect PSUs (despite that the obscure barrel connector is probably only 19.5v systems anyway), most certainly it’s a crappy design to not inform users. To fail to assign an error code. Sure, it vaguely says in the manual something like “use only approved HP power adapters” -- something /smart/ consumers do not take seriously because they know how to match PSUs to appliance and know that shit is always a branding hussle. The data pin should not be a secret that is concealed from both the user guide and the maintenance and service guide (which HP says is not for end users.. yet they still withhold the info from service people).
Perhaps good design as far as the PSU goes. But shitty to not document the situation and to not implement an error code.
¹ I stress /may have/ prevented damage because I have seen a lot of street market goods and only seen this obscure barrel tip on HP and Dell laptops, both of which are 19.5v.