You just need to provide either 5VDC, 9VDC, or 12VDC (depending on which model meters you buy) to the meters. Kal's doorbell transformers reduce 120VAC to 12VAC and they are easy to procure. Then the adjustable power supplies convert the 12VAC to whatever DC voltage required, from 2.5VDC to 27VDC.
You could of course use your own power supply. If you bought a 5A 12VDC power supply and made sure you bought the 12VDC version of those panel meters you don't need the doorbell transformers.
Here is an example of a 220VAC 5A 12VDC power supply on ebay for just over $10: LINK
You'd still need 2 of them though to isolate the meters per Kal's instructions.
Here's the other issue: Kal provides detailed instructions on how to wire everything up. If you buy something that he doesn't recommend, I wouldn't anticipate finding much information on how to wire your device. Although it is fairly simple. You hook up 220V to the AC input and you hook a meter up to the DC output.
As a last note, you could either ditch the meters altogether, since they aren't required for anything, or you could buy an all-in-one power meter like I did and ditch the power supplies and transformers altogether. The power meter itself is huge, but not much bigger than both of the smaller meters combined. The power meter is 96MMx96MM as opposed to roughly 79MM by 84MM combined area of the 2 meters. The big difference is the depth of the power meter is 80MM as opposed to the 24MM of Kal's meter recommendation. This wasn't an issue for me because my panel was huge, but it may be a problem for people who have their panel already planned out. Here's a picture of my panel with the power meter installed and on: