I am trying to drive a single XML T6 with a spare 5v 2A adapter. It runs fine but I noticed the cable heat up considerably. Is the heat coming from the extra 2v ? Is that safe to run such condition?
I'm assuming you are not direct driving this?
You need a regulator, constant current, preferably one that does not dissipate the extra energy as heat.
6-18V 3000mA 3-Mode Circuit Board for XM-LT60 Emitters
5$ at DX. There are other options.
An XM-L pushes more than 2A at 5V, so right now your adapter is being run pretty much in 'fault' mode and might as well be shorted. It won't last long (the adapter).
Easiest way to drive a single XM-L is with a DC/DC driver as per listed above. You then feed the DC driver from an appropriate source, which is typically any 12volt adapter with sufficient amperage.
If you want to drive multiple XM-Ls there are other options.
The Mean Well looks like it's designed to drive another driver downstream. Fixed voltage in this circumstance won't help you.
For driving multiple XM-L's Mean Well makes a whole pile of AC drivers in the 2-3amp range. Not sure where to start.
For DC/DC applications looks at some of the flashlight drivers on Kaidomain or DX that Purduephotog mentioned.