I'd say **no, don't do it**:

- **The shorter url isn't worth a lot**. We're talking about a absolute minimum abount of value. Rephrazing one sentence is worth more.
- **You have collected an amount of backlinks**. Backlinks have to be redirected, loosing a bit of SEO value in the process, and the anchor itself looses some juice
- **You give up an domain that exists for quite some time**. An old domain has value as it is some indication about the reliability (based on "if it's  crap, it wont last long").
- The `.supply` domain isn't that common, it might confuse people
- All the people who remember your url now remember an old url

What you can do is the other way arround, make the `.supply` be an alias for de `.com`, a little geeky extra feature.