mains earth and op-amp ground
simulate this circuit &ndash; Schematic created using CircuitLab

Figure 1. What you've done.



Figure 2. What you're not accounting for.

The power supply has capacitive coupling between the high-voltage side of the transformer and the low-voltage side. This occurs through the transformer capacitance and the deliberate capacitance circled in Figure 2. The effect of this is that the PSU output has a weak alternating voltage on it. You might be able to read this with a digital multimeter between one of the terminals and the mains earth.







simulate this circuit

Your op-amp has a very high input impedance and is very sensitive to over-voltage. Most likely is that the capacitively coupled voltage exceeded the maximum allowable input to the op-amp.