That may indicate that the Java installation used by your Jenkins on WIndows does not recognize the SSL certificates that Let's Encrypt provides for the Jenkins update center.
Check the Java version from the "System Information" page in "Manage Jenkins". Java 8u262 is the most recent version of Java 8. Java 11.0.8 is the most recent version of Java 11. If you're not running one of those versions, download and install a version of AdoptOpenJDK for Windows and modify the Jenkins configuration to use that new Java installation.