Over the past year, JWST has uncovered galaxies at record-breaking distances up to z ∼ 13. The JWST UNCOVER (ultra-deep NIRSpec and NIRcam observations before the epoch of reionization) program has obtained ultra-deep multiwavelength NIRCam imaging of the massive galaxy cluster Abell 2744 over ∼ 45 arcmin^2 down to ∼ 29.5 AB mag. Here, we present a robust ultraviolet (UV) luminosity function derived through lensing clusters at 9<z<12. Using comprehensive end-to-end simulations, we account for all lensing effects and systematic uncertainties in deriving both the amplification factors and the effective survey volume. Our results confirm the intriguing excess of UV-bright galaxies (M_UV < -20 AB mag) previously reported at z>9 in recent JWST studies. In particular, a double power-law (DPL) describes better the bright-end of the luminosity function compared to the classical Schechter form. The number density of these bright galaxies is 10-100 times larger than theoretical predictions and previous findings based on Hubble Space Telescope (HST) observations. Additionally, we measure a star formation rate density of ρ_SFR = 10^-2.64 M_⊙ yr^-1 Mpc^-3 at these redshifts, which is 4 to 10 times higher than galaxy formation models that assume a constant star formation efficiency. Future wide-area surveys and accurate modeling of lensing-assisted observations will reliably constrain both the bright and the dim end of the UV luminosity function at z>9, which will provide key benchmarks for galaxy formation models.