Mixer Audio output xlr small contact with pin power suply of guitar pedals , possible damages?
More than likely that PSU has no reference to ground. You can confirm this by checking the mains cable. An oval / flat cable or two-pin plug or plastic earth pin (depending on country) indicates that there is no earth connection.

If this is the case the power-plug is similar to a battery. It is floating with respect to ground and touching one point of it to another circuit will do nothing as no (significant) current will flow.







simulate this circuit &ndash; Schematic created using CircuitLab

Figure 1. Various power-in scenarios.


In (a) the battery negative has been connected to the input. Since the positive is not connected no current can flow.
In (b) the battery positive has been connected to the input. Since negative is not connected no current can flow.
In (c) there is a complete circuit so DC will be applied to the circuit. Even in this condition 12 V is unlikely to cause any damage as the input capacitors will block the voltage after the initial transient.


The flick on the VU meters is probably due to some capacitance between your power-supply and ground. I would not be concerned about damage.