Studio 540 PSU questions/additional dvd drive

im interested in what type of PSU should i look for when upgrading the more details into the the type of PSU the better for example 20pin 20+4pin 24pin etc all the goodies just want to be 100% sure. Oh i got another nub question just to be careful i dont want to damage my desktop but how do I safely remove the metal plate blocking the second cd/dvd drive so i can install a second drive just bought this thing and dont need to break anything yet lol wonder y it came with such a lame PSU though well thanks in advance for any help