there is no such thing as "pop-punk" for that would be a contradictory statement of the two opposite energies of the universe.
what it really is is "Modern Punk", just like rock punk has changed for nothing remains the same and people need to except that. it is punk fused with an element of just having fun playing music.
PUNK IS NOT DEAD, IT JUST CHANGED.
The Cure and The Who and Lou Reed are key influences in the genre of (for sake of requirement) " pop-punk ".