this case is conductive, precisely so the excess charge can be grounded by the power supply by being in touch/contact with the psu metallic casing. the psu is

this case is conductive, precisely so the excess charge can be grounded by the power supply by being in touch/contact with the psu metallic casing. the psu is grounded, but the static has no way of getting to ground (via psu) if the case itself is non-conductive.