What kind of problems are you having? How old is the rack? I've read that API changed the power trafo some years ago to a beefier toroid.
Open yours up and see what's inside. The old one, AFAIK, is PCB mounted. If it's a new rack, you should have no issues, they should support the max 130mA per rail per module.
Don't buy into the API PSU bashing you may see online, if they were that bad, you would see them all failing before their 5 year warranty was up. It's a good company, they make good stuff, but like any other company are subject to accountants' cost-cutting more than we are here. But they can't afford to make something sub-standard, especially when it's their standard.
Anyway, if you have an old rack with the old trafo, call API and see if they'll swap it for you. Probably beyond the 5 year warranty, but you never know if you get someone on a nice day.
I've never seen the 600B PSU, but I have seen a BAE lunchbox PSU, which is marketed as higher current and capable of powering 2 full racks, which I think is a bit of an exaggeration. It's a simple LM317/337 PSU, not much different from the SSL9K PSU you get from gustav, though I don't remember if their toroid had a separate 48V winding for phantom or used a voltage multiplier like the SSL.
If you are having no problems, make yourself some tea, relax and forget about it. Work on something else.
If you are having problems and API can't help, you can always get yourself a 3 rail PSU and a 2x16V, 40-50VA toroid and wire it yourself. Cheaper than a rack, and you still get the portability of the API, which is the best part about it.