Supernovae do not turn into Red Giants or White Dwarfs. You have things a bit backwards.

What holds a White Dwarf together is something called "electron degeneracy". This does not mean that they lost their morals. What it means is that as gravity overwhelms a Red Giant and compresses it, it fails to make enough density to create any heavier nuclei and the spaces between the atoms have been reduced to zero.

However, electrons do not like getting that close to one another and they put up a fight, having enough strength to hold the carbon and oxygen nuclei into a stable state. At this point the electrons cannot go up or down in energy levels and they fail to absorb or emit any energy..They are "locked" into such a state.

If more mass is dumped on the white dwarf the electrons react by vibrating at a higher and higher frequency. With more and more mass being added (by either some binary red giant companion that has expanded beyond its Roche Lobe limit or by some dense star dust field within a galaxy or 2 dwarfs merging) the electrons reach a limit.

Special Relativity sets a limit to the amount of vibration for the electrons. They cannot reach or exceed speed c. Once the white dwarf reaches a limiting mass of 1.4 solar masses, the electrons give up and runaway nuclear reactions are set off as the star becomes unstable. Fusion starts taking place all over the star and neutrinos are created in enormous numbers, enough to create collision events with practically all falling gases and any gas envelopes. Half of the star's mass fuses to a radioactive isotope of nickel, Ni56 which decays into unstable Cobalt-56, then into Fe-56. These decay processes emit gamma rays that bounce around inside the exploding star and are converted to optical light.

Basically the supernovae (Type 1 in this case) is a neutrino event and not a plasma event. Even the plasma gets blown away by the neutrinos AFAIK.