It works well as power supply, with or without being plugged in since the batteries do their job well. The battery compartment cover has a usability issue though: one needs a screwdriver to open it. Also, the batteries are somewhat loose inside. It comes with rubber legs which are to be glued on place.
One major thing to note here is that this box is useless without preamplifier. I found this out the hard way. One shouldn't generally do that but a decent dynamic mic plugged in to line input is actually louder than a phantom powered small-diaphragm condenser coming out from this power supply and connected to the same input.
The item gives me the impression of being bare or rough: plain metal box with battery hole and unpolished wooden battery compartment inside. And yet, it does its job and it does it well.