If that 300w is a high quality one, then it may be enough (if it came with a case it's probably a cruddy one however). If I was getting a new PSU I'd want 350w or so from a high quality mfg. Fortron, Antec, Enermax, etc.
here is my 2cents worth right here. First Get rid of that stock 300w ps. It is more than likely a generic one that will last him if he is lucky a year at most.
Now, with that being said here is what I think you should get for him.