The Surface Pro 4 dock doesn't seem to charge properly when it's fully drained, which means the charger has been unplugged for months. After some searching I needed a regular travel charger which I didn't have. Order this and I now have a travel charger that charges this bad boy and it's quite small and light. The USB connector on it appears to be USB2.0 only, but makes it a good connector for a mouse transponder, and you can use the built-in SP4 USB connector for storage if needed. It's also fairly cheap, about a third the price of a stock OEM charger.