Would really have to come down what a reasonable consumer would expect; that is part subjective and part objective. If you could show an experience of having laptops for various lifetimes, some extending beyond 7 years some below, none having a failing power socket, that might be sufficient to convince that it is a major fault. If it is a cheap laptop maybe you don't have a chance, but a premium product you could argue that it failed to be durable.

(I read this as the power socket in the laptop, not so much the power supply, obviously you'll have less luck there.)