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.