First off DE has nonresident taxes due on the S corporation income.  This does not apply to 1065 income. On the SCT-RTN (formerly 1100S) form it should calculate.

Next, you have to enter manually the Column B, line 10 amount on the PIT-NON for rents, royalties, partnerships, S corps, etc. and report the actual DE source income (in your case the $150k).  Column A would show $50k since it's the Federal amount.