You become a resident of Delaware for tax purposes on the day you begin living there with the intent of making it your permanent home. Your residency is not determined by your drivers license or voters registration. That's because some people wait months (or even years) after moving before getting their new license or registration.
PA can tax all the income you earn as a PA resident. PA can also tax you after you move and become a DE resident on income you earn from physically working in PA, and on income from work you do remotely for a PA employer - if that work is done remotely for your own convenience. This PA tax reference explains:
https://revenue-pa.custhelp.com/app/answers/detail/a_id/3599/~/how-are-telecommuters-wages-taxed-in-...
Once you become a DE resident, all your income becomes taxable by DE, regardless of where you earn it.
You may claim a credit on your DE tax return for the taxes you pay to PA on income that is also taxed by DE. This protects you from double taxation.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
