Re: Universal power supply for PCs, setting voltage

On Sun, 3/30/2025 11:55 AM, micky wrote:
> I probably don't need a universal auto power supply, but otoh, if I'd
> bought one for the last laptop, I wouldn't to spend 30 or so dollars for
> another one now. 
> 
> Some of them have 3 wires connecting the tips, one to tell the power
> supply what voltage to provide, I assume, but others have only 2.  How
> can that be satisfactory. 
> 
> This one, for example.  
> https://www.amazon.com/HKY-Universal-Notebook-Computer-Smartphone/dp/B0BZGSMLMP/ref=sr_1_1_sspa
> See the first picture.  But it's $44, one of the most expensive.  How
> could it not work right? 
> 
> 
> 
> https://www.amazon.com/Belker-Universal-Adapter-Charger-Toshiba/dp/B08LKXDBX3/ref=sr_1_1_sspa
> Smaller than most.  Are they just trying to trade off the name Belkin? 
> 
> At first I thought it had to be good because it was Belker, but when
> writing this post, I remembered that it's Belkin that has a reputation,
> not Belker.  !!  
> 
> 2)  Some have 50W, 65W or even 100W.   What could need 100W?   I
> currently have a Dell Latituded 5510 (not the other Dell 5510).  Surely
> 65 w is enough or even 50. ????
> 

  Car 12VDC ----------- DC-DC converter ----- USBPD ---+---- USBC output (uses USBPD protocol)
  Lighter Socket?                                      |                 (for USB port charge)
                                                       |
                                                       +--- dumb charging, fixed voltage,
                                                            barrel adapter

I don't know if the adapter works in those rental cars
with the plastic cover.

The USB PD output option is likely safe.
The charging speed will be a function of whether
the laptop even has USB PD protocol. If the adapter were to output
5V @ 1A for example, the laptop will use a boost converter
inside, to charge a 14.4V battery pack. If a higher USB PD
voltage can be negotiated, it might take only
a buck (down) converter inside the laptop, to charge the battery.

For legacy laptops, this kit proposes to charge
via a barrel jack. Does it actually output the correct
voltage ? I would be concerned about that. There was
evidence previously, that the voltage uncertainty on barrel
charging was fairly small (even though from an engineering
perspective, it's not necessary for that voltage to be
all that tight). I would still be a bit nervous about
barrel charging, unless the product had a way of selecting
18.5V, 19V, 20V, or whatever the listed spec for the
laptop is. I do not want to recommend solutions to people,
that only burn out the charge management in a laptop a month
later. That's what happened in at least one case here.
That was the anecdotal evidence, that a mismatch on
barrel voltage, put something under stress. Someone visiting
had a shit eating grin on their face, over the "universal"
product they bought. A month later they wrote back to say
the laptop would no longer charge, with anything.

If you have a USB PD laptop, go for it. Otherwise, do not.

H11: 16V 4A 6.5*4.5mm 19.5v 3.3a 4.7a 6.5*4.4mm
     So the barrel adapter H11 works with both a 16V laptop
     and a 19.5V laptop ??? Most of the other barrel tips are playing
     the close enough game, when they might not be close enough.
     It could just be using a fixed 19V output when the USB PD
     protocol is not detected. The advert is pleasantly unclear
     on the matter.

   Paul