Yes, you can add more then one YouTube Channels in Adsense account, because Google does not allow more than one Adsense account so, you can easily add multiple YouTube channels in one Adsense account without any restriction.

It is possible to use one Adsense Account for multiple YouTube channels. All you need to do is link your YouTube channel to the intended Adsense account. You can add as many as you want.

How to Add Two or more YouTube Channels in Adsense account?

1. Sign in to YouTube Studio.
2. Select the Monetization tab on the left menu.
3. Click on the Sign up for Google AdSense.
4. When prompted,  re-authenticate your YouTube account if required.
5. Now, sign into the Google account used with your existing AdSense account or Create a new Adsense Account.
6. Continue setting up your account.

After following these above steps, you’ll be taken back to YouTube Studio, where you’ll see that your Adsense account successfully linked to your YouTube Channel. If you Set up for New Google AdSense you will need to wait once your account has been approved, which can take up to several days.