I think the sentence should be: Oyu o tsukaeru sentakuki no pawaa ni kandou shita otto wa おゆのつかえるせんたくきのパワーにかんどうしたおっとは oyu o tsukaeru sentakuki = washing machine that can be used with hot water / that you can use hot water This O is a particle for the object "oyu" because the user uses oyu. You can also use GA for the object which is with the potential form of the verb. "~ni kandou suru" is an expressio for "to be impressed with / to be touched with". I think your question is like "why is WITH used here?". In this case, WITH is translated into NI. (It's BY of "to be excited by" if you translate it with "excited".) Since I'm not an expert of the Japanese language though I'm Japanese, please wait for the better answers if you need more details. I hope this was helpful.