They may have switched the hot and neutral inside the wall, on most things like lights, fans, and aquarium pumps it wouldn't matter or even show up, but on electronic equipment it can cause problems with things like phone chargers, comp batteries, cable boxes ect...
A rectifier changes AC (alternating current) to DC (direct current).
Unscrew, or unplug the block. They may have left the cover plate on the receptacle, so it may have to be removed too. There are either 3 or 6 wires in the receptacle, most of the time the receptacles will be daisy chained together inside the wall, so if there are 6 then don't freak out. take the two screws out at the top and bottom of the receptacle and slowly pull it out of the box. A black (hot 120volt), a white. (neutral), and a ground (just a bare copper wire). if it's the last in the chain (only 3 wires) you may have to check them all in that room because it may be wired incorrectly in the receptacle before it.
On the receptacle there are screws on the side where the wire is landed. One should be copper color, this is where the black wire goes, the other side should have a silver screw, this is where the white wire goes, the bare copper wire should be landed on a screw that's in the mounting bracket of the receptacle. the fin size or the grounding prong usually means you can't mess this up, but if they wired the outlets wrong you may be feeding voltage to the device from it's neutral fin which on a lot of things doesn't matter, .
how many things do you have plugged into the block, because a voltage drop (normal 120 volts, but with 5 other things running may be as low as 90 it could affect the rectifier. (you can check that with the meter if you get one, this is what I think is probably the issue with you.)
if you do buy a meter read the book, but there is a setting on it that looks simular to this "~" that's a/c, the d/c setting looks like this "- - - ". The meter, unless you spend big bucks on it, it is probably not auto ranging (the one in the picture Caeli posted isn't), so make sure it is set over 200 so you don't blow a fuse in the meter.
black wire- will shock you.
white wire- can shock you, but probably won't, if there is voltage there it probably won't be enough to even feel it.
ground- won't shock you
I wish I lived close enough to check this out for you, but I hope this helps.