from google there are some elite 311 that came with 400w psus (mostly foreign sites, which could explain the OPs english).
tom's hardware thread indicating some models shipped with a 400w psu at some point in time/space
http://www.tomshardware.com/forum/342225-28-best-cheap-case-list
the current 311 can come with a 420w psu.
http://www.coolermaster-usa.com/product.php?product_id=3066
without model numbers it's pretty hard to determine if the power supply is any good.
based on the naming scheme of the case + 420w version, i'm going with RC-311B-BKR400
this leads me to the power supply being called the TM-400W, which probably means thermal master 400w, which is probably a cooler master branding for their case + psu combos
closest i can find is the tm-420 probably the current 420w psu packaged with the 311
http://www.coolermaster-usa.com/upload/download/380/files/TM-420W.pdf
if you can take some pictures of the power supply or give us all the numbers printed on the power supply it would help.
There are actually no pictures of a Thermal Master 400w, and I haven't been able to find anything about it online, so I don't know if this model actually exists. It may just be termed that, but actually be some other PSU.
If there aren't any external labels, try to get information off the fan, or try to get pictures of the internals.
There are coolermaster cases packaged with the cm elite 400w. This might be one of those.
if this is an elite 400w it's probably either Solytech or FSP/Fortron
http://www.jonnyguru.com/forums/showthread.php?t=10970