I found this the other day, which allows me to use all of the Dell power adapters I own (for Latitudes and Precisions but other Dell adapters with 7.4mm connectors should work) with my XPS 13. I've been using mine for a few days without problems. I didn't keep track of whether using this with a higher wattage power adapter resulted in faster charging, and I suspect it doesn't because of the thermal design tolerances of this thin laptop. I typically carry a standard Dell adapter for my work laptop, so now I only need to carry one adapter regardless of whether I'm carrying my personal XPS 13 or not.
http://accessories.us.dell.com/sna/productdetail.aspx?c=us&l=en&s=dhs&cs=19&sku=331-9319
Here's a picture:
