If your original door bell chime is a solid state electronic chime rather than an older style electro-mechanical chime, there is not enough current available to charge the ring doorbell. If your existing doorbell is DC powered rather than AC it is not compatable with Ring which needs AC.
If your door bell plays a melody rather than a ding-dong sound, it is an electronic chime. Check the Ring set-up instructions, there is a procedure for solid state electronic chimes. If it is an electronic chime it may be necessary to replace it with an electro mechanical chime and AC transformer