I have a generic 300W Enermax PS (comes with the Enermax case). It powers 1 FDD, 1 Super Dish LS-120, 1 SCSI 2GB Jaz Drive, 2 CD Drives and 4 HDDs (1 SCSI, 1 IDE, and 2 others IDE in RAID-1) . Supposedly, it's too much for the PS to handle, but I've been running it for more than 2 yrs without any problem (1.2GHz Athlon T-bird).
Many times the drives had run almost full load i.e. I burned some stuff (both CD Drives were running) while I listened to music from RAID-1 drives (both of them must run at then same time) and surfed the net (SCSI drive is in use), or I moved data from other IDE drive to RAID-1 drives. NO PROBLEM SO FAR.