Potato salad is a popular dish in Japan too. It is offered at izakaya taverns throughout Japan as single dish but hard to find at other type of eateries. You may encounter potato salad as a garnish, placed on together with meat or fish. Therefore if you want to try Japanese style potato salad, you have to go to izakaya or buy it at supermarket and eat it at your hotel.
Japanese potato salad uses mashed potatoes, not potatoes cut in cubes or sliced. Then, mayonnaise is added. Also usually ham, boiled eggs, cucumbers, carrots, and onions are included to. Sometimes you can find apple too.
Many nationwide izakaya taverns serve already made potato salad coming from food factories, therefore if you prefer homemade ones, better to visit small local taverns. These taverns would serve signature potato salads adding other ingredients than mentioned above.