how do I find the right cable for it?

How to choose the right cable for your laptop
1. For most of the modern models laptop which support USB Type-C power supply. Select the USB C2C cable.

2. For other laptops that use traditional (non Type-C) power adapters. Choose a proper converter cable. Make sure the connector shape & size is exactly same as your original charger's. And also the output voltage is in the same range of your original one's.

You can use following two methods to find out the dimension.