The Dart-C is fully compatible with the latest USB 3.1 standard that is used on Apple MacBook and MacBook Pro, Lenovo ThinkPad 13, ASUS ZenBook 3, and Dell XPS 13. You can charge these computers at the fastest possible speed.
The 60-watt NuPower can quickly charge most popular laptops under 14 inches. It will take around two hours to charge the 13-inch MacBook Pro (2016), only slightly longer than using the original 61 W adapter.
You will not be able to use NuPower as a replacement for a more powerful adapter. For example, if you use it on a 15-inch MacBook (2016) instead of the original 87 W charger, it will at best prevent the battery from draining, but not increase the charge.
If you own a laptop that is bigger than 13 inches, you should definitely check if the wattage of this adapter is high enough for your computer. It wouldn't be able to replace a charger with power output over 45 W, so it won't charge a 13-inch MacBook Pro, for example.