Objectives: In this study, we aimed to evaluate the effect of post design on the push-out bond strength (PBS) of self-adhesive resin cement in simulated flared root canals. Materials and Methods: A total of 135 specimens simulating flared single root canals were fabricated using standardized 3D-printed resin (FREEPRINT^® CROWN; Detax GmbH, Ettlingen, Germany) and allocated into three groups: single, double, and customized glass fiber-reinforced posts (Pillar Fiber Post, TiaDent, TX, USA). All specimens were cemented using self-adhesive resin cement (Rely X^TM U200, 3M ESPE, MN, USA). The specimens were then sectioned perpendicular to the long axis into coronal, middle, and apical slices, each measuring 3 mm. After thermocycling, they were tested for their push-out bond strength. Failure modes were analyzed using stereomicroscopy. A statistical analysis was completed for PBS data using a two-way ANOVA test, and failure modes were analyzed using a Chi-square test at a significance level of α = 0.05. Results: We observed statistically significant differences in the PBS between test groups (p = 0.044*). Double-post specimens exhibited the highest PBS values at the coronal section (8.26 ± 1.54 MPa), followed by the middle section (7.77 ± 1.73 MPa). Across all root sections, the PBS of double posts (7.58 ± 2.07 MPa) significantly outperformed customized (6.76 ± 1.15 MPa) and single-post (6.73 ± 1.75 MPa) groups (p = 0.029*). The coronal third (7.44 ± 1.54 MPa) consistently showed higher PBS compared to the middle (7.15 ± 1.64 MPa) and apical (6.49 ± 1.90 MPa) thirds (p = 0.027*). Failure mode analysis revealed that customized posts predominantly failed at the post-adhesive interface, whereas double posts showed a mix of adhesive failures and single posts demonstrated more adhesive failures at the canal walls. Conclusions: The use of double fiber posts significantly enhances push-out bond strength in flared canals compared to single or customized posts. Relining techniques improved canal adaptation, but the performance here did not surpass that of double-post configurations. Clinically, the double-post approach may present a simple, practical and effective alternative to improve the bond strength of fiber-reinforced posts for flared root canal systems.