Anything where the eccentric is accentuated can strengthen tendons (which is why it is used in physical therapy when you have tendinitis).
Super high reps help sending more blood to the tendons (which are less vascularized than other tissues) helping them recover.
Both of these approaches will work my improving the structural aspect of tendons. And to a point it will thus make them stronger.
Overloads (heavy partials reps, heavy negatives) will desensitize the Golgi Tendon Organs which will tone down your protective mechanisms which will allow you to produce more force.