If you want to increase your power to the body -weight ratio, or relative strength, then the best way to improve your pullups is to do more pullups.
Are weighted pull ups/chin ups bad for your shoulders? - Quora
How many pull-ups should I be able to do before adding weight? - Quora
5 Pull-Up Alternatives You Can Do At Home (No Bar) - Fitplan Blog
The Top 10 Accessory Exercises For Pull Ups — Accelerate Strength
kevinyxng (@kevnyang)
Weighted (Dumbbell) Pull ups - Learn the Exact Form
Pull-up vs. Chin-up: Muscles Worked, Differences, and Variations
Cali Studio
James Kew - The Physique Coach - Pull-ups are one of the best exercises you should be doing to build a strong back. Pull-ups are great because they allow you to challenge