As a core component in ultrasonic vibration systems, piezoelectric transducers play a crucial role in various application scenarios. Although spherical transducers have high application value in fields such as underwater acoustics and structural health monitoring due to their perfect three-dimensional omnidirectional radiation characteristics, traditional structures generally face many technical bottlenecks: limited sound intensity and power capacity, fixed and unadjustable electromechanical characteristics after the device is formed, and severe acoustic impedance mismatch with the radiation medium. To break through these limitations, this paper systematically reviews the latest research progress on novel spherical piezoelectric ultrasonic transducers and piezoelectric transformers, focusing on representative structural innovation work. First, a cascaded spherical transducer structure is introduced, which alternately composites metal spherical shells and piezoelectric ceramic spherical shells in radial space, effectively increasing the total effective volume of piezoelectric active materials and achieving high-intensity, wideband, and perfect three-dimensional omnidirectional acoustic radiation. Second, a stacked spherical transducer is introduced, which radially stacks two piezoelectric ceramic spherical shells with opposite polarization directions and sandwiches them between metal layers to overcome the excitation difficulty of thick-walled piezoelectric ceramics; compared with the traditional structure, this configuration drastically reduces the first-order equivalent electrical impedance of the system by 84%, while increasing the radial vibration displacement to 1.26 times that of the traditional sandwich spherical transducer. Third, an electromechanically tunable spherical transducer is introduced. Without changing the basic geometric dimensions of the device at all, the design dynamically reconstructs the total equivalent impedance of the system through external electrical loads such as resistors, inductors, and capacitors, successfully achieving a wide range of frequency tuning capability and significantly broadening the operating bandwidth of the transducer. Fourth, a spherical transducer based on 1-3-2 type piezoelectric composite material is introduced. This design effectively solves the impedance mismatch bottleneck by introducing low-acoustic-impedance high-molecular polymers into the spherical shell structure, which not only effectively suppresses interference modes but also significantly improves the acoustic radiation efficiency of the system. Fifth, a novel spherical piezoelectric ceramic transformer (SPCT) operating in the radial vibration mode is introduced, which fills the blank in the research field of spherical transformers by realizing bidirectional voltage conversion with both step-up and step-down outputs and optimized power gain. Ultimately, this review demonstrates that these structural innovations effectively break through the performance limits of traditional piezoelectric ultrasonic devices; in addition, this paper also prospects the future development trend of piezoelectric transducers evolving toward intelligent "sensing-computing-driving" integrated systems and micro-nano structures, providing a solid theoretical foundation and technical paradigm for the innovation and development of a new generation of advanced ultrasonic vibration systems.