Excuse the topic bump, if anybody are still looking for a supported Let’s Encrypt client on Windows it’s worth checking out my own app Certify The Web: https://certifytheweb.com which is a full GUI for LE certificate management on Windows. The app is free to use but has a paid version for commercial use and where support is required. The app has been going since 2015 and has many thousands of users (in the region of 200K downloads) including many .gov.* installations.
The reason I felt it worth commenting here is Windows users are often businesses (or large organisations) and are therefore specifically looking for supported products (over free, but unsupported tools), it can also be pretty difficult to find proven solutions that are continuously maintained.
While the app is typically used on a Windows Server with IIS, the next major version will have new support for Apache, nginx etc and unlimited deployment tasks (local or remote) including deployment to remote services over SFTP/SSH. Beta testers wanted! https://github.com/webprofusion/certify/issues/440