It’s from inside the laptop’s port. It’s (sort-of) required because there are at least three contacts between the charger and the laptop: hot (+20V or something like that), ground and data (the charger tells the PC its power rating). On the barrel plug, these are on the outside of the barrel, on the inside and the third is the pin in the middle.
The piece exists to guide the barrel plug inside the laptop’s port and to prevent you from accidentally bending its contacts.
I recommend you get the laptop’s port repaired before charging it again. Because the power port is a low-tech part and Dell laptops are quite serviceable in my experience, this should be a relatively cheap repair.
If you absolutely must charge your laptop before you can get it repaired, you should insert the plug very carefully, centered and perfectly straight. Otherwise, you could bend any of the now-exposed contacts, making charging impossible and possibly causing a short-circuit.