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I have

  • a DELL XPS 13 9370 with a DELL H754V84 battery that can only be charged using a USB-C port.
  • a USB-A > USB-C adapter
  • a USB-A charger. It can output 9.0V 1.65A or 5.0V 2A

Can I safely use those to charge the laptop's battery?

The computer requires 20V (2.25A) but surely the USB-A -> USB-C adapter can give the proper voltage, even if it charges slowly, right?

  • Please edit the question to include the EXACT type/model of zBook. – Tonny Apr 12 at 12:15
  • Done. Copied the laptop's and battery's references, not sure if it's a zBook anymore. – Dune Apr 12 at 13:10
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    A zBook is a HP device. Now you are talking about a Dell computer... Totally different brand. – Tonny Apr 12 at 13:11
  • I might be wrong, but I would have thought that a USB-A power supply that provides 9v is off-spec and potentially dangerous. USB-PD only works on USB-C? – Attie Apr 12 at 14:29
  • What kind of "adapter" do you have? Does it have Type-A recaptacle, connected via a short cable (or no cable) to Type-C plug? Or is it a cable with plugs on both ends? – Ale..chenski Apr 13 at 6:41
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Your laptop uses Type-C charging port, and it is made after 2016. Therefore it must use only PD (Power Delivery) as a standard means for voltage/power negotiation, per specifications for Type-C connector. I assume that Dell is a USB-IF certified computer, so the PD is the only acceptable protocol, and the communication must use CC pins.

If your "a charger" has only Type-A receptacle, it can't have PD since there is no CC pins in Type-A port. Therefore the laptop won't be able to negotiate fast charge, and likely refuse to take the default 5V level.

Now, if you will try to experiment with various Type-C to Type-A adapters, be careful not to plug Type-C to Type-A receptacle adapter, aka "OTG adapter". It will turn the laptop into host function, and the laptop will OUTPUT +5V on VBUS. If you will try some combination of cables and manage to connect it to your charger anyway, there will be conflict of power supplies, with unpredictable outcome. Don't do this.

The only chance your laptop will charge itself is if you have a charger with Type-C non-detachable cable plug. People reported that 30W PD chargers do work with XPS 13 9370, but issue a software warning that power supply is suboptimal for full performance.

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USB-A to USB-C adapters normally DON'T adjust the voltage. They are normally just a cable with 2 different connectors on each end.
To adjust the voltage there has to be an additional DC-DC converter somewhere and a chip that negotiates with the USB-C port which voltages are offered.

So most cables only just take the 5V, 2A from your USB-A charger and pass it straight on the USB-C port.
This is not going the charge the battery. Charging will always take more than 5V as the charging voltage needs to be somewhat higher than the output voltage of the battery.

Most likely the laptop thinks no charger is attached. Maybe it will draw some power from it for normal operation of the laptop thereby reducing the load on the battery, but it won't charge the battery.

You shouldn't be able to do damage by trying but be VERY CAREFULL to plug the charger in a real USB-C port, not in one of the Thunderbolt ports! Thunderbolt also uses the USB-C connector but they are NOT charging ports!

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