I adjusted the PSU to 14V because that's what Prusa did with MK2 when it was launched and it was suffering from temp faults when using the part cooling fan. Their fix was to tune the PSU to 14V. I haven't checked the PSU on my original MK2 (now MK2.5), but I assume it's running at ~14V.

You might be correct about lowering the voltage back to 12V, though. It's obvious that 14V is overkill for the MK42 bed, especially with RAMPS. Also I'm using a silicone sock on the hotend so lower voltage shouldn't cause problems with it. Also as I bought the E3Dv6 directly from E3D, it might be that it has a more powerful heater cartridge than what MK2 was shipped with.

Still, the printer has been working fine so far, no blown fets since I restricted the bed power in firmware.