Hello@Elisabeth , 

Thank you for being interested in tp-link powerline devices, powerline units need to paired under the same powerline circuit /under the same power meter, and devices communicate with each other through house powerline.  A power station could provide power but could not build a powerline environment that the powerline KIT need. 

If you need to build a wireless connection from main building to garden building, you may need some outdoor products, it is recommended to create new thread under business products sub-froum from here (better include the distance, the garden office building is indoor/open area , the number of clients)