|If you're simply trying to measure how much electricity is used by the aforementioned servers, you do not need to network them together.|
Plug them all into the same PDU (power distribution device) and measure how much they use.
Most of the PDU's we use in our server racks actually have an LED display that tells you how many amps are being used by all devices plugged into that PDU.
As far as "stressing" the servers goes, have them all perform a disk defrag at the same time. That will max out the disk(s) and should load up the CPU.
Loading up the CPU and HDD's of the servers won't increase the load on the PSU's. That should remain constant unless you change hardware. For example, put a high performance gaming video card in, or two in SLI. Short of changing hardware, the load on the PSU's won't differ.
Also, you need to check and see what kind of PSU's are in the servers. In a typical dual PSU setup, one is a redundant and it will have minimal load. Which is to say, using just enough power to make the LED light green on the back of the PSU. The load of the running hardware inside the server will be on the primary PSU. I've seen a few blade type servers that have 3 PSU's. Two that "load share" and one redundant backup.
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.