If the Power2U is seated too deep into the electrical box or the outlet is not parallel with the wall, these spacer shims are needed behind the outlet screws to bring the outlet forward so the faceplate can seat flush against the outlet.
If the faceplate is not flush against the outlet, the shutters may not depress the switches when plugging in a USB cord.
A faceplate will not seat flush against the outlet if the Power2U is seated too far into the electrical box or if the outlet is not parallel with the wall.
Spacers twist apart easily for desired thickness.