Different voltage on powerbank

[Phineas12]

Hello, I have an hp elitebook 640 g9 and the ac adapter has charging output of 19.5 volts, now I want to buy a powerbank since this device has less than half battery life vs. advertised despite battery saving mode, and also it does support power delivery on type c, but all I can see in the stores are 20 volts. Can I use these powerbanks despite the voltage difference? upon searching I saw that 5% margin in voltage is ok on modern laptops but I also saw some who said this can damage the laptop, now what?

[erico]

In all electrical and electronic voltage specifications there is an allowable deviation of +-5%.

20 Vdc is not OK for USB type-C, unless you mean 20 Vdc input for charging the power bank.

USB Type-C power banks for adapters should provide 5Vdc output for the laptop

However, you should make certain that a power bank is compatible with your laptop before purchasing it.

As an example, the power bank at the hyperlink is an HP product but it does not list compatibility with your laptop.

https://support.hp.com/hr-en/document/c05742765

[Phineas12]

Hello, I couldn't quite follow, my device requires at least 45 watts of power, and I've seen lots of usb c chargers that has 20 volts at 2.25 amps output, does that mean I also can't use those kinds of usb c chargers? Why is it ok with 19.5vAc chargers but not 20vdc? Thank you for answering , I'm quite new to this stuff

[erico]

If the power bank can supply at least the wattage that the power adapter your laptop was delivered with that will work.

I did not say that 20 volts would not be OK.

You did not understand that what I said applies to any electrical or electronic device. 

The 19.5v that is stated on a device means that it will actually deliver between 18.5 and 20 Volts DC. That is an acceptable tolerance.

"I've seen lots of usb c chargers that has 20 volts at 2.25 amps output"  That is 45 Watts.

Did you mean to say power bank instead of "charger"?

The power delivery has to be 45 Watts or greater.

Any of these in the article except the one delivering 18 Watts, will work with your laptop

6 Best Power Banks With USB Type-C Power Delivery - Guiding Tech