Quick charging interuptions when plugging in

[BauDemo]

When plugging in a Think with Gen1 PCU to the outlet the charging is interrupted several times (4-6 times) in quick succession, and then the charging continues.
During this period a noise (like leaking capacitor?) is audible.
Once the charging starts there is no problem and the car is charging ok. This occurs only during the start of the charge.

During the interruptions the diagnostic equipment is reporting unusually high AC input voltage - 250VAC. When the charge starts the voltage is reported normally - around 230VAC.

Any ideas what this could be?
What can we measure or check?

Could it be something with the isolation transformer and the soft starter for it (in the floor behind the driver) or is it something in the PCU?

[jur]

Just guessing, but I would suspect some resonance phenomenon between transformer and the AC line input filter within the PCU. I've seen 2 of these filter PCBs (from Gen0 and Gen1) damaged beyond repair by severe arcing back in 2014/15 (had photos posted here, but can't find them right now). I wondered then, what could trigger such arcing, but toggling the transformer instead of soft-starting would be a plausible candidate.
I could think of 2 tests to gather more insights:
- connect the transformer secondary to a robust load (lamp, resistor etc.) and check power-on behaviour with an oscilloscope.
- bypass the transformer and connect the AC input of the PCU directly to the grid (of course taking extra care of possible ground faults and live voltages within the car), then check behaviour at power-on.

Regards,
Jens