Well, CAA may also be a problem, but the error message here isn't that CAA forbids it, but the CA's policy. I'm guessing that dell.com is on their list of highly-important-but-not-yet-using-LE names that requires manual intervention on Let's Encrypt's part in order to allow.
If you're actually authorized to issue certificates for dell.com (that is, their IT is adding Let's Encrypt to the CAs that they work with), you'll need to go through the process listed here to remove the block (in addition to updating or adding CAA records):