I have the same XPS One A2420 and box to sell. What is safe way to wipe out hard drive, and is this difficult to do with just "home owner skills?"

Coluccio

I've found DBAN, very effective for erasing all the data from a hard drive.

Go HERE for more information.

You could also, perform a clean reinstall of the operating system, this would wipe the hard drive as part of reinstalling the operating system.

Bev.

DBAN has aged and is not good especially for SSDs you are best to use Parted Magic and then manually clean install Windows 10 RS1. Follow my guide which will take you through both - step by step:

http://dellwindowsreinstallationguide.com/cleaning-up-a-drive-format-vs-secure-wipe-ssd-and-hdd/ 

http://dellwindowsreinstallationguide.com/download-windows-10-oem-and-retail-iso/