Higher power rating is fine -- the system will only draw as much power as it needs.  
Replacing a TB16 with WD22TB4.  For reasons too mudane to detail, it would be immensely more convenient to plug 240W power supply currently attached to TB16 in the new WD22TB4, instead of installing the 180W power supply that came with the new dock.  Is it safe and effective to do so.  Have found nothing online that addresses this.
WD22BT power supply question