Do you mean you only want certain types of websites to appear on your Adsense code on your website?

That will naturally happen if your meta tags, and on page optimization is done properly. The Adsense code will naturally take care of targeted ads as much as possible

To display adsense ads, you must put Adsense codes somewhere on your site. Those codes will derive ads from Google AdWords, and display the ads relevance to your site contents if they had the relevance ads.

No matter who you are, the codes only inspect your contents and display ads that is relevance to those pages that your visitors viewing.

For example:
- You put Adsense codes in website aaa.com which is focusing on weight loss. Therefore, the Adsense codes will be displayed only the ads related to your contents in website aaa.com. Sometimes, it also display the irrelevance ads, too.
- You put the same Adsense codes in website bbb.com which is about home rent. The codes will dynamically display the ads according to the contents in website bbb.com which is home rent related ads.
- The same situation will be happened in another websites of yours that you put the Adsense codes, too.

In some sites, the ads also display irrelevance, too. Because either it doesn't have the relevance ads or you contents is lack of focusing words or in general.

If you do good SEO then this will happen anyway.

Using custom channels inside your Adsense menu can solve your problem I think.

I think you are not talking about adsense, you are talking about Adwords. Are you looking to advertise your website or looking for targeted advertisements in your website?