Yes Wing Chun Punches are design to be fast,take up space and with the entire body behind it an jing accompanied to it a knock out is very possible.
Three keys
1.Time and Placement
2.Correct Body alignment
3.Right Power and Right Force
You need to be able to hit the person at the right place with the right amount power to shock their nervous system an cause them black out. Also if you continously wail on them in the same place continously they will not be able to recover.
Your WC should also have different ways of generating force. From the motions Found in Chum Kiu for Yip man lineage or the motions found in the San Sik in mainland lineages. Since San Sik is given to beginners you learn how to generate power with your horse early on. From shifting to stepping forward.
The force your body exerts as you lunge forward like in Biu Ma coupled with Jing and powerful snapping force is more than enough to knock someone out if you can get a clear and open shot.
The Flow is relentless like a raging ocean with crashing waves devasting anything in its path.
"Kick Like Thunder, Strike Like Lighting, Fist Hard as Stones."
"Wing Chun flows around overwhelming force and finds openings with its constant flow of forward energy."
"Always Attack, Be Aggressive always Attack first, Be Relentless. Continue with out ceasing. Flow Like Water, Move like the wind, Attack Like Fire. Consume and overwhelm your Adversary until he is No More"