Hello I have a question regarding consumer electronics. Suppose I have a Li-ion portable charger. The input says USB C 5VDC 3A, 9VDC 2A. What charger would be the best to charge this charger? Would a USB-C charger that says Output: 5VDC 3A, 9VDC 2A (exact match) be the best fit? How would the device charge? Would it alternate between 5VDC 3A and 9VDC 2A? How many times would it alternate between charging ratings? Because if a different charger, a 15W USB-C charger with the single specification of 5VDC 3A was used to charge the device, how would the device charge? Would it use only the input rating of 5VDC 3A? And would that be a better charge rate to preserve the life of the battery? (Since it will charge at only 5VDC 3A , (15W)). Would the higher current degrade the battery or the higher voltage? 5V 3A would be lower voltage but higher current than the 9V 2A. So maybe a 9V 2A only charger would be better? Just wondering the best and safest way to charge this. And the way that preserves battery life. Thanks

Product is described here

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    \$\begingroup\$ what do you mean charge a charger? ... the device in each picture is a power supply, not a charger \$\endgroup\$
    – jsotola
    Jan 16, 2022 at 4:14
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    \$\begingroup\$ Hi. Thanks for your reply, I wasnt able to post the 3rd picture of the Li-ion portable charger/power bank due to the file size being too large. The power bank's input is USB-C 5VDC 3A, 9VDC 2A. The power bank is just another term for this portable charger, which can charge a phone or laptop, etc. I am familiar with electronics but I just don't know enough about it to figure out what the optimal way to charge this is. As for the pictures I attached, how would the white one (Insignia) charge the power bank since it has the same power ratings that the power bank's input asks for, or is it unknown \$\endgroup\$
    – Bus gas 12
    Jan 16, 2022 at 6:02
  • \$\begingroup\$ IMPORTANT I have edited your post to show the two images that you mentioned in links. I have removed the image which did not APPEAR to relate. Please check and confirm that what I did is correct. | Your question did not seem to make sense with the old image. It makes SOME sense with the new image. More detail will be required to make the question clear. \$\endgroup\$
    – Russell McMahon
    Jan 16, 2022 at 12:07
  • \$\begingroup\$ @jsotola Please see images and my comment. \$\endgroup\$
    – Russell McMahon
    Jan 16, 2022 at 12:09
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    \$\begingroup\$ Despite what it says on the label, that's a power supply, not a charger. It will output a fixed voltage after negotiation by the attached device. The charge controller will be in the device (phone, tablet, etc.) and will regulate the voltage and current to its battery to prevent overcharge, fire and explosion. \$\endgroup\$
    – Transistor
    Jan 16, 2022 at 13:59

2 Answers 2


I'll try to simplify this. 5Vdc/3A ,9Vdc 2A are simply the specification for the technology called USB PD (power delivery). The portable device would communicate with the charger to provide the desired output, either 5V or 9V. However, one should be careful to ensure that the devices are compatible and prevent unintentional failure. Therefore, I would highly suggest that the recommended charger, as per the portable unit technical documentation is used. Otherwise, the unit may be damage, and the warranty could most likely be void. P.S. A portable charger is a unit that is used to charge portable device and also needs to be change.

  • \$\begingroup\$ i.stack.imgur.com/89HbU.jpg Hi thanks, \$\endgroup\$
    – Bus gas 12
    Jan 16, 2022 at 6:08
  • \$\begingroup\$ Please see new images \$\endgroup\$
    – Russell McMahon
    Jan 16, 2022 at 12:08
  • \$\begingroup\$ Thank you everyone for the answers. I really appreciate it. \$\endgroup\$
    – Bus gas 12
    Jan 17, 2022 at 16:31
  • \$\begingroup\$ Hi everyone, I am using a wall adapter with USB-C 5V 3A, 9V 2A output to charge it. As Passerby has mentioned, it is most likely using the 9V 2A rating. I believe this because both the wall adapter and the power bank device have that rating. (Wall adapter has 9V 2A output, and power bank device has 9V 2A input). It is charging as I type this and the wall adapter is warm, but not hot. Thank you for all the information and answers. \$\endgroup\$
    – Bus gas 12
    Jan 18, 2022 at 21:59

Based on the new picture, you have a basic USB-C PD device. It can charge at 18W via 9V 2A or 15W via 5V 3A. The 18W is faster for the battery to charge from. Just use a suitable usb-c PD power supply that has 9V 2A output. They will all have a 5V out per USB standard.

The power bank will negotiate the 9V PD from the charger and will not alternate until its disconnected or the PD negotiation fails. The 5V is the fall back voltage. PD works by active communication between the source and sink.

  • \$\begingroup\$ IMages were wrong. See new images \$\endgroup\$
    – Russell McMahon
    Jan 16, 2022 at 22:52
  • \$\begingroup\$ We call it a "Power Bank". We charge our cell phones with it. In China maybe they use it as a power supply. We charge its internal battery from USB 5V. In China I do not know where they get 9V to charge it from. \$\endgroup\$
    – Audioguru
    Jan 17, 2022 at 16:50
  • \$\begingroup\$ @audioguru what? \$\endgroup\$
    – Passerby
    Jan 17, 2022 at 17:16

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