Hi @mannermauler ,
Here’s a link to the [https://downloads.dell.com/manuals/all-products/esuprt_laptop/esuprt_inspiron_laptop/inspiron-17-3721_owner%27s%20manual_en-us.pdf|service manual] for your laptop, taken from this [https://www.dell.com/support/home/au/en/aubsdt1/product-support/product/inspiron-17-3721/manuals|webpage]
Scroll to p.73 to view the necessary pre-requisite steps and then the procedure to remove the ''power adapter port''. (Their name for the DC-In jack)
Replacements are available online, just search for ''Dell Inspiron 17-3721 power adapter port part'' to get results. Here’s a link to just one [https://www.parts-people.com/index.php?action=item&id=15269|supplier] of the part. It is shown only to give you an idea of the cost of the part and also the various Dell models that the part is compatible with.
Hopefully this is of some help.