Apple's MacBook has fewer configuration options than Dell's XPS 13. That's important to note because, while the starting price of the XPS 13 is a lot lower than the MacBook, the laptops get closer in price when the specs are more closely aligned.
Specifically, the starting price for the XPS 13 is $800, which gets you the non-touch display, 4 GB of RAM, 128 GB of storage and an Intel Core i3 processor. The starting price of the MacBook is $1,299, for a model with more RAM (8 GB) and storage (256 GB). When you outfit the XPS 13 with comparable RAM and storage to the entry-level MacBook, the price goes up to $1,099 (though this also gives you the Core i5 processor). Getting the MacBook with the Core i5 processor brings the price up to $1,399. So essentially, when the spec configurations are as close as possible, you'll be paying $300 more for a MacBook than the XPS 13.