First, you need a Hulu account with subscription.
Then, open your browser's console before click play on any shows. When start playing, search smi on the network tab.
Copy the link of the *.smi file, which looks like this:
https://assetshuluimcom-a.akamaihd.net/captions/751/61464751_US_en_en.smi
This is an encrypted file. But now, we can get the WebVTT version of this. Change the link to something like this:
https://assetshuluimcom-a.akamaihd.net/captions_webvtt/751/61464751_US_en_en.vtt
You're all set!
WebVTT to ASS or SRT. For Windows, just Download Subtitle Edit.
You can use command like this:
SubtitleEdit /convert source.vtt ass SubtitleEdit /convert source.vtt srt
Personally, I think ASS version is better than SRT. The program will keep format tags like <i> in SRT, but works perfect in ASS.