I just tried inverting electrode polarity (still with the voltage set as 265V, but I haven’t checked in practice if it’s still the same—will do later and probably increase it) and applying electrolysis and I noticed some strange effects.
If I immerse the (now) small-area anode slowly, current is very low (0.02A from the multimeter, no increase in AC mode from the current probe) and a persistent “ball” of water forms around it. Electrolysis does not seem to occur to any significant extent. If I further immerse the anode, this phenomenon disappears and regular high-voltage electrolysis starts, with current increasing to substantially higher levels. I think I need to increase voltage to start seeing a plasma.
I've made a video of the process with the camera on a tripod, and it's a bit blurry, relatively long (3 minutes) and probably boring. It's unlisted.