How to charge an usb-c equipped laptop from a powerbank

I have got a laptop that can only be charged via usb-c.

I also have a powerbank (45000mA) that not only has usb outputs, but also an output (up to 20V) for laptop charging. It came with 11 adapters for all kinds of laptops and additionally an old macbook connector. But it does not have an adapter for usb-c charging.

Would it be possible to create an adapter with one of the available laptop adapters, an usb-c connector and some wire? What would the cabling have to be like?

Answer

This is not about making "own wire". Since you have Type-C laptop, you need to make your powerbank compliant to Power Delivery specification.

It can be done by designing some in-line "adapter", with 20-V input on one side, and power delivery on the output side, with Type-C cable at the end.

You will need to design this board by yourself. There are several IC manufacturers who offer Power Delivery chips/kits, to negotiate and supply higher voltage to a laptop. Here is an example of solution offered by Texas Instruments. You will need to implement the block shown in RED square in the following diagram, on the right:

This block will provide Power Delivery interface to your Type-C laptop. It is a one-chip solution.

You will also need to implement a variable DC-DC converter, to convert 20V from your powerbank to a variable (5-9-12-15-20 whatever) for delivery, circled in RED. The DC-DC converter will be controlled by the above PD interface chip. The suggested design of this variable supply is given here. Keep in mind that PD must start with "safe +5V" level, and only then negotiate and enable higher charging voltages. If you apply 20 V upfront, without any PD protocol in place, the laptop will unlikely to accept the voltage. Well-designed laptop will do nothing, and a bad one may fry itself.

This is what it takes to make your powerbank to charge your Type-C laptop. Somehow I doubt that this process will cost you less than a different powerbank with already built-in PD over Type-C.

EDIT: I linked wrong PMP11451, it is a full AC-DC design. But you must get the idea.