The ones I've seen don't, no. The AS/400 boxes were pretty much designed for small-to-medium-sized businesses to stick in a closet and forget about. You may be thinking of IBM mainframes, which typically require three-phase power, but can be convinced to work without it.

These days (and for quite a while), the boxes that run IBM i are the same POWER servers that can run AIX and Linux. Before the platforms consolidated, they were still POWER servers, it was just a different firmware between the "i Series" (ran OS/400) and "p Series" (ran AIX and Linux) POWER boxes.