This paper investigates the transient performance of grid-forming (GFM) converters during power reference regulation. It is revealed that implementing fast power control induces a rapid fast voltage source behavior, which, however, compromises the GFM capability. Furthermore, the decoupling control of active and reactive power responses leads to larger voltage magnitude fluctuations, thereby sacrificing the ability to maintain a stiff voltage source. To address those trade-offs, an adaptive control strategy is proposed, which is activated only during power reference regulation to achieve fast and decoupled power control. The GFM converter, utilizing the proposed control method, successfully achieves fast power regulation while minimizing the power coupling. Both simulation and experimental results validate the theoretical analysis.