Dual PSU Servers - Startup power draw?

Hi

My understanding is that with Dual PSU servers both PSU's draw half the load required and share the internal supply to the servers internal devices.

However, during start-up is this still the case OR does the server draw from one PSU during the start-up phase and only draw on both PSU's when started?

I think the first part of that is correct where both PSU's always share the internal load of the server BUT I'm constantly being told that during start-up just one PSU is used, this seems illogical to me and I'm sure its wrong but....

Anyone throw any light on this?

Cheers

Leon