Power steering box locks up at low RPM

Did it not do that before the alignment? Did you just replace/repair a suspension part?

I'm thinking they adjusted the lash in the steering box. Did you complain the steering box seemed loose? They wear more in the center so, it could be too tight when you turn it off center. Go back and ask them.

Do you have a Federal/Eaton round filler neck pump? I've had those loose assist making quick low speed maneuvers.

Or it needs a rebuilt pump.