Jelqing involves stroking movements that compress blood in the corpora cavernosa and expand them under pressure. The grip isn’t tight enough to prevent some blood from slipping through as the stroke moves toward the glans. Jelqing strokes are usually done the full length of the penis.
Uli’s exercise involves clamping the base of the penis to prevent any blood movement out of the shaft after using Kegel’s exercise to pump it full and short (one inch/2.5 cm) strokes which creates a tremendous increase in pressure. Many use a “Uli thing” or clamp to keep blood in the shaft while doing Ulis.
Here is a post I made which contains links to the original posts on Ulis and other “head” exercises.