i have an HP Envy 17 and the charger died, no output. so i connected a DC power supply that has Volt and Amp sensing,
The original charger has three wire connection, to the pc power point, white black and blue...
after searching the web, the blue wire is a sense wire... in effect the PC and Charger can determine what is required, check if the connector is powered, disconnected etc..
i connected that blue sense wire to the white wire ( plus V )
so.. with that done i owered up the pc with the completely different supply source, the minimum V that seems to work and be stable is 18.V but ive tried up to 19.4, i choose to keep the lower V because its seems to be all that is needed.. and unlikely to cause damage in consequence..
with the PC up and running, the current ( which is determined by my power supply ) can vary and fluctuate, seldom is it more than 2 to 2.5 amps briefly, and never drops below about .75 A
to see if the battery in the PC was being charged, i shut down the PC, but left the supply connected... the current settled to 1.62 amps at 18.1 V and stayed like that...
after about 10 minutes i powered up again, and the battery charge had increased from 58 to 68 percent..
so not only was the PC happy.. i could charge its battery..
so... you need a supply that can automatically vary its current output upon demand, not a constant current output, because you will overcharge the battery.. and also constant current might harm some components which might overheat..
but yes... another PSU can do the work.. mine isnt a cheap Laptop its over £1000 to replace,
This particular PC needs a 120W HP power supply... when i can buy one at a good price i will replace it , and now i know it doesnt have to be an HP one...
but for the pc to detect properly since that blue wire does that its not just about V sense ... i will probably use an HP one of the correct Watt type. . pretty much that means i`m only using my own psu to do it while i am there with the PC until i replace the original.
Update 13 october 2018: after putting the pc to sleep, my psu rapidly charged the battery to 100 percent. at that point the psu current demand had fallen to 75 mA on waking up the pc, everything was functioning all aok..
of note, 18.1v is the minimum required... and to stop the switch over by the pc from psu supply to battery, ( something it does automatically, ( dims the screen a little on battery saving, full brightness on psu ) i had to raise the supply v to 18.8v
i think my battery is beginning to age.. since upon waking the pc, this morning 12 hours plus later, with the psu connected but turned off, the battery condition had fallen to 54 percent, maybe some of that loss is because the psu was connected but turned off - current leak? and the rest just the pc components drawing power over those hours, i.e it wasnt shut down, but sleeping..
with the psu turned back on, the current demand needed is just below 1A to just above 1A at 18.6 V, it seems ( probably because of the way the pc sensing operates ) it is only charging the battery when in sleep or shutdown because i get the window on the screen giving the battery status, and it says "not charging" until when i shut down the PC , with the psu on, the current rose to 2.9A and the V to 19.1v for about ten minutes, then as if a measuring point had been reached it suddenly switched to 1.53A and 18.6 V
the battery is over 6 years old now... so its not unexpected that it isnt as good as it was..
any way - end of story... i hope this exercise helps anyone...