Hi Nicolas ,
the problem is if you disconnect the DC supply to the G540
the E stop in the AC supply to the power supply
is just another on/off switch thats easier to switch off in a panic
the E switch connected to the PC will stop the stepper motors quicker
provided the PC is still responding
but the E stop in the mains supply is guaranteed to stop every thing
once the stored energy in the power supplies has been used up
http://www.homanndesigns.com/pdfs/EN010_V8.pdf
John