What is the origin of the name "Caf-Pow"?

It's a fictional drink supposed to be rich in caffeine but in reality it's just a Hawaiian Punch or cranberry juice and a parody of 7-11 drink.

From answers.com:

Caf Pow is a parody of a 7-11 'Big Gulp' it's size and coloration match almost exactly to the well known brand. Big Gulp cups at a 7-11 can be filled with any soda or juice available on their soda fountain. At the time the show started 7-11 was carrying an energy drink which matches the color and appearance of caf-pow on their soda fountains. The drink is called 'Wild Stallion' and it could be purchased in a Big Gulp cup. Wild Stallions orange mango flavored drink in a Big Gulp cup is the closest you will find to the 'Caf Pow' the character is drinking in the storyline. (even though its not what the actress is drinking when playing the part). Wild Stallion uses extract from coffee beans; however it is not coffee because it is never brewed and the extract is removed by pressing instead of heat (the way coffee is made) so it is considered a juice and not an iced coffee.

On trivial note:

According to Perrette, the cups were originally filled with Hawaiian Punch, but when she stopped eating and drinking refined sugar, unsweetened cranberry juice was used in its place. - Wikipeida

I can't find any source of how did they came up with the name yet but as from Google search I can see the definition of pow as:

expressing the sound of a blow or explosion.

So naming a drink which is supposed to have x-treme caffeine caf-pow make sense.

Although it's hard to know for sure it's probably a mixture of "Caffeine" and "Power" although the "POW" might also be a play on words for an indication of the impact the caffeine has on your system.

If you look at the image you provided...you can see the words "X-treme Caffeine" right there on the cup.

Caf-Pow is a high energy-caffeine drink that NCIS Forensic Scientist Abigail Sciuto is regularly seen drinking as it's her favorite brand of drink and it also gives her the caffeine high she gets from it as it helps her get through the day while completing the many tasks she has to do.

^Wikia

Caf is obviously for "Caffè", but what's the "Pow" stand for?

Other answers provide some context, but honestly this—at least to me being in the U.S.—is quite a simple thing.

First and foremost, it’s a fake brand created for a TV show that simply wanted to have something that implies a real consumer item but without actual branding being connected to it.

And yes, the “Caf” is a shorthand reference caffeine and the “Pow” can be inferred to mean “Power.”

But honestly it immediately seems to be a play on words that is designed to invoke the classic visual sound effect known simply as… “Ka-Pow!”…

I always assumed it was an homage/made-up version of Jolt Cola based on the color scheme and the emphasis on the extra caffeine.

Note the the product names are in white, the lightning bolt/exclamation points are yellow, background is red, etc.