I have two WS-C3750X-48PF-S in stack, but every one has just one power supply. In the package of the switches is included one stack power supply cable.
my question is , does it make sense to use stack power cable if every switch has just one power suppy ??
Stackpower gives you the option to share the Power Supplies between all stack memebrs (Max 4).
There are two configuration modes for StackPower, Redundant Mode and Shared Mode.
In redundant mode, as t relates to your situation, one PS will be in standby while the other PS will provide power to your two switches within the stack. Keep in mind it is important to ensure that you have enough juice with one PS to power up both switches and all you attached PoE devices...This is when Cisco Power Calculator comes in handy. http://tools.cisco.com/cpc/PDS.cpc
In Standby Mode, all PS are active but if one PS has a surplus of power it can distribute the surplus power to power up devices attached to any port within the switchstack. This is a good setup if you have PoE devices but they are not evenly distributed within the switchstack. It also provides redundancy in case a PS fails, but once again you need enough juice for this.
See this good read from Cisco in regards to StackPower.
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It think it does if the individual power supplies have enough capacity to power the stack of two if one of the power supplies fail. Even if they don't if the stack supports prioritization of power shedding (i.e. with insufficient power, you select what loses power first) (don't know if they do), then it can make sense too.
If the individual power supplies are insufficient to power the dual stack, you might only need to add 3rd (and 4th?) power supply but it could be smaller wattage then what you have now.
Absolutely it does.
This is a POE switch wich makes it possible to draw much more power than the smallest powersupply can generate.
so depending on powersupply you might even have to use the stackpower if there are to many poe+ units on the same switch but almost none on the other. Also if one powersupply breaks down you can choose wich of the switches you want to stay alive or you can choose ports to shutdown so that you can have both switches alive on one powersupply.
so basically what you can do with the powerstacking and poe is
Priorotise ports to stay alive ie tech guys phones might be more valuable to stay alive than salesforce.
or the APs might be more valuable than phones or vice verse.
you can also Priorotise switches to stay alive ie one switch handles more important units than the other and this you can keep this unit up even if this units powersupply is the one that breaks down.
Share power between units. if one ps is not supplying enough for the total switch then it can get help from the other ps in the other switch.
So with POE+ switches absolutely there is a point in using the powerstack cabeling.
I can find no drawback with using the stackpower over not using it.
To find out more about how to configure it se the links from Tironevi above.