I just purchased a Dell XPS 15 and I found that the 10% "PCs and Dell electronics" coupon I recently received in the mail stacks with the 15% "PCs and Dell electronics WHEN YOU FINANCE" coupon, which means that you can get 25% off. (I don't think they're supposed to stack with each other normally.)
To do this:
-I entered the 10% code on the Cart page.
-I proceeded to the Payment page and set the payment method to Dell Financing.
-I returned to the Cart page and entered the 15% code.
I ended up with the highest build level of XPS 15 (i7, Windows 10 Pro, 1 TB SSD, 32 GB RAM, GeForce GTX 1050, 4k touch display, fingerprint reader, 4yrs Premium Support, 36mo LiveSafe) for $2004.68 before shipping/taxes/environmental fees (expedited shipping was free). I had an employer discount as well; without that, it would have been $2,045.59.