Purpose: The primary objective of this randomized, double-blind, placebo-controlled study was to investigate the acute effects of caffeine from various sources (1. gel, 2. chewing gum, and 3. capsule) on muscular strength and power in resistance-trained individuals. The secondary objective was to directly compare the magnitude of caffeine’s effects (at the same absolute dose of 300 mg) from different sources on muscular strength and power. The tertiary objective was to examine the impact of caffeine on muscular strength and power and compare these effects with the placebo effect on one hand, and with the control measurement (measurement without supplementation) on the other. Methods: Jump performance was assessed through a bilateral countermovement jump test on a force measurement platform. Lower body strength and power were assessed on an isokinetic device. Upper body power was assessed using the bench press exercise at 50%, 75%, and 90% 1 (repetition maximum) RM with the assistance of the PowerLift iOS application, while whole-body power was assessed using a rowing ergometer test. The tests were conducted over seven laboratory visits during which participants, before testing, consumed: (a) caffeinated chewing gum (300 mg) or placebo chewing gum; (b) caffeinated gel (300 mg) or placebo gel; and (c) caffeine capsules (6 mg/kg) or placebo capsules. In the segment investigating the effects of caffeine from capsules, one laboratory visit consisted of testing without any prior consumption (referred to as the “control measurement”). The participant sample size varied across different study segments, ranging from n=16 (age (mean ± SD): 22.9 ± 2 years) in the segment investigating the effects of caffeine from gels to n=26 (age (mean ± SD): 24.2 ± 5 years) in the segment investigating the effects of caffeine from capsules. Results: Compared to placebo chewing gum, caffeine from chewing gum acutely improved (by 3-9%) countermovement jump performance, lower body strength and power, upper body power, and whole-body power. Consumption of caffeine from gel acutely improved (by 3-12%) all the previously mentioned strength and power dimensions in comparison to placebo gel consumption. There was no difference in the magnitude of caffeine’s effects between gel and chewing gum sources on muscular strength and power. Caffeine from capsules significantly improved (by 3-8%) vertical jump height, lower body strength and power and upper body power compared to the placebo capsule and the control measurement. Caffeine from capsules acutely enhanced (by 4%) whole-body power compared to the placebo, but not compared to the control measurement. Although the placebo generally did not exhibit an ergogenic effect compared to the control measurement in most tests, such an effect was observed in two tests (countermovement jump, bench press exercise). Conclusion: The consumption of caffeine from alternative sources (gels, chewing gums) can acutely enhance jump height, lower body strength and power, upper body power and whole-body power in resistance-trained individuals. There are no differences in the magnitude of acute effects of caffeine on strength and power when considering caffeine at the same absolute dose consumed from different sources. Therefore, the choice of caffeine source for individuals interested in caffeine supplementation appears to be a matter of personal preference. Finally, in certain tests of muscular strength and power, placebo consumption was ergogenic compared to the control measurement, indicating the presence of a placebo effect that should be considered both in scientific research on caffeine as an ergogenic aid and in the practice of physical exercise and sports training.