i have a bunch of rectangular plastic capacitors usily come from power supplys. are these ceramic, mylar, tantalem, paper or other.
are thay of any real use to me as a hobyist?

 

Why don't you post some photos of them? Or if you can't take a photo, find images of similar capacitors on Google Images.

 

Hard to tell what they are just from your description.

Post a picture where one can see what's printed on them.

Yes they may be of use if you are mounting your own electronics projects.

 

Depending on what you are doing everything might be of value

 

the first picture shows what i was originaly talking about.
the 2nd is also somthing i have been wondering about also i beleve the ones in the second pic are mylar but not sure.
if you could tell me what eather or both these are thanks