Namecheap hosting does not offer Let's Encrypt SSL certificates, however, all of the hosting servers allow their installation. So you may obtain a Let's Encrypt SSL and install it on any server with Namecheap.
AutoSSL will be available to Namecheap customers through Let's Encrypt starting on May 2nd, 2019.
Namecheap is unable to support AutoSSL because it was developed using the https only protocol which is not compatible with their customer's email service.
