Abstract: To improve the controllability of ultra-high-frequency welding current waveforms, the topology and control sequence of a multi-branch ultra-high-frequency pulsed welding power supply were optimized. By adding an independent constant-current branch and adjusting the branch combinations, multi-level current waveforms with adjustable amplitudes, sequences, and durations can be generated within a single cycle. In addition, a snubber circuit was incorporated into the high-speed switching branches to improve the output accuracy and stability of complex current waveforms. An experimental platform for arc observation and welding tests was established. High-speed imaging, narrow-band filter imaging at 696.5 nm, and Abel inversion were employed to obtain the arc morphology and temperature field under different current waveforms, and welding tests on IN718 sheets were conducted. The results indicate that, at an average current of 90 A, the arc width and contour area generally decrease with an increase in pulse frequency, and the high-temperature region gradually concentrates toward the arc column center. At 100 kHz, the arc width and contour area of Wave4 decrease by 15.67% and 20.28%, respectively, compared with the direct current condition; the area fraction above 14 000 K reaches 21.34%. The weld penetration reaches 2.17 mm, representing an increase of 50.28% over the direct current condition, and the average grain size in the weld center decreases by 39.5%. The optimized multi-branch power supply can output complex ultra-high-frequency current waveforms, and the regulation of arc morphology, temperature field distribution, weld formation, and grain structure can be achieved by adjusting the amplitude combinations and temporal distribution of current levels within a single cycle.