Types of capacitors

[electronics-whiz]

I know some of the capacitor types, but others I'm still not sure just looking at them.
I can tell an electroletic, supercap, ceramic disks, tantalum caps.

I'm not sure though about the plastic rectangular/box looking ones. I know there not electrolytic as are not marked and found in AC input stages. Then there are ones that are also rectangular but are like plastic coated and have curved edges. I always called both these Mylar caps, but I'm not not sure that is right as I can't see why they'd use a different case style.

Am I right, if not what are these capacitors?

[TimFox]

You probably mean plastic-film capacitors.
There are two common types of film, with a few others.
1.  Polyester or PET:  Mylar is a trademark.  Reasonable performance (Q roughly 100 to 200).
2.  Polypropylene:  Excellent performance (Q roughly 1000).  Tends to be larger than polyester for same capacitance.
Most film capacitors now are metallized film: very thin metal deposited directly on both sides of thin plastic.
Film-foil capacitors have actual metal foil separated by film, for lower ESR, with increased size.

[tggzzz]

Have a look at http://eevblog.com/files/seekPDF.pdf