Some of our Blade Specialists give us the workings of the BladeSystem "Power switch" . David gives us these words of wisdom.

"I've always referred to the "power switch" on the front of the blade not as a power switch but a " may I?" switch.  When actuated, the blade asks the OA if there is enough available power to power on and spin up the drives (the act of powering on takes a higher load than steady state operation).  If at that moment there is not enough power, the blade pauses and tries again in a moment (there's an algorithm in there that determines the actual length of the pause so that if several blades had asked for power at the same time, they don't all use the same delays and end up in deadlock).  If after requesting power several times (sorry, don't know how many) there still isn't enough power, it will stop trying. If a blade has not been successfully turned on, the command can be issued again.

Net/net:  the blade infrastructure is designed to prevent more power demand than is available.  The illustration above is equally valid if power-on is initiated from power switch, OA/iLO command, or via Wake-on-LAN..."

And Tony added in his experience.

"David is correct but there are some subtleties about how the server will respond.  On a cold boot - insertion, enclosure power-up, etc. if Automatic Power-On is set, then the server will retry power on requests if they get denied.

Power-On commands like the power button or iLO Virtual Power/OA commands are one time things - if the request fails it will not be retried.  Therefore as David said the application needs to be able to detect if a server has powered on after the request is issued."

Hope this helps.