Hello Johanna, welcome to the Forums. Although the PD-15OUT outdoor plug will be rated for this transformer-controlled load, since it is just an on and off control, unfortunately the dimmers included in this kit (dimmer model PD-6WCL) are not rated for MLV dimming to control magnetic transformers. We do not recommend using a non-MLV dimmer on an MLV load, to protect the longevity of the dimmer and transformer and to prevent performance issues. The best Caseta dimmer to use for magnetic low voltage loads is model PD-10NXD. This device requires a neutral wire connection for MLV loads and will look the same as the current dimmer:
www.lutron.com/TechnicalDocumentLibrary/369919_WEB.pdf
We hope this helps!