DNS-prefetch is an attempt to resolve domain names before resources get requested. If your website opens connections to many third parties, prefetching those domains can help to reduce latency.
The URLs that entered the field will be converted to protocol-relative URLs (//) when adding the hint.
DNS Prefetch and Preconnect
PoweredCache automatically adds preconnect hint when entering URLs for dns-prefetch. The difference between dns-prefetch and preconnect is; preconnect establishes a connection to a server. This process includes DNS resolution, establishing TCP connection, and performing TLS handshake if the requested connection uses SSL.