The X-ray fluctuations and spectral characteristics of two fascinating kinds of jetted Active Galactic Nuclei (AGN)—blazars and Fermi-detected Narrow-line Seyfert 1 (NLSy1) galaxies—are thoroughly examined in this work. In the first section, we highlight a two-decade-long X-ray monitoring of several notable blazars: Mrk 421, 3C 273, and PKS 2155-304, revealing interesting multi-epoch, spectral, and temporal patterns. We investigate the intricate interactions of jet dynamics through in-depth examinations of flux variability, hardness ratio changes, power spectral density (PSD), and bi-modal flux distributions. Spectral modeling using different non-thermal components challenges the conventional blazar paradigm by revealing, for example, in 3C 273, the appearance of a thermal disc component co-existing with jet emission. 

In the second section, we focus on jetted NLSy1 galaxies, separating disc and jet contributions by integrating NuSTAR, XMM-Newton, and ZTF data. The identification of thermal disc fingerprints in the soft X-ray and optical bands, cases of pure jet-dominated X-ray emission, and evidence for disc-jet coupling are discussed. The accretion-jet relationship in these low-mass, high-accretion AGN is uncovered using a variety of X-ray timing and spectral approaches. In a nutshell, these findings demonstrate the highly variable, stochastic X-ray behavior of jetting AGNs and the value of multi-epoch, multi-instrument studies in revealing the physics behind them.