AC or DC ? ?
I would only weld with DC. After having a Lincoln buzzbox for yrs, I upgraded to a miller DialArc 300 AC / DC and what a difference it makes on DC welding stuff.
Now, a very, very helpfull tool is the grinder. gets some abrasive flap wheels, instead of the disk's. They really let you know if your welding penitrated (after grinding the weld off) and what type of job you did.
Preperation is key, key, key. Reguardless of what welder/rod, getting the surface / crack prepped correctly is key (did I mention prep is key)?
Adding additional supporting steel is optional, after proper prepperation of the weld area.
Best thing to do with welding is practice, practice and more practice. I'll get junk steel out in the winter and Prep it, then weld on it. Build up, welding seams together and such. Grind off the welds to check penitration and such also . . . .
If it holds, you did good, If it breaks - well, you get to try again. Prepping the weld area first.

Edit: Looks like a lincoln buzz box . . . The best rod for that is a 6011 rod. Key to 6011 is a kind of tapping motion into and out of the puddle. It's a fast freeze rod. I can weld down with it better then welding up. I control the puddle when welding down, where as when welding up, seems that puddle gets too liquid when coming back into it.
Your welds should look like nickles stacked into each other . . . ..