Stop the Resupply is a side quest in The Darkspawn Chronicles DLC for Dragon Age: Origins. It is a part of the main quest Massacre in the Market. The Denerim guards are trying to rearm themselves; stop them from doing so by blowing up their weapons cache.
Once the genlock sapper has destroyed the Alienage gates, the Archdemon will warn you that the guards are trying to resupply themselves. Head north to Wade's Emporium. The merchants Wade and Herren will be in the small alleyway between Wade's Emporium and the Denerim Chantry. Kill them and all other guards and soldiers. Once the area is cleared, click on the weapons cache in front of the Chantry. The genlock sapper will automatically move to it and set it to blow up.
The quest Slay the Healer triggers.