Dips are a great way to build upper body strength, stability, and pressing capacity. However there can be many mistakes for positioning and range of motion in the movement. The pictures on the top are using stable bars where the lower pictures are using rings.
-Notice how in both of the left hand pictures the body is in a hollow position or concave with the core engaged and feet in front to help with balance. This hollow position allows for greater range of motion in elbow flexion which leads to the shoulder getting below the elbow without as much stress on that joint.
-The pictures on the right are showing the body in a straight line pushing the body forward past where the hands are created more extension and pressure in the shoulders and putting them in a weaker pressing position. This also limits the range of motion.
Try to keep your hands neutral like you are sliding them into your pockets. Next time you are doing ring or bar dips try these tools to have better technique which will lead to more reps and/or strength in this movement!