TESB shows us a puzzling picture of power generation. Fusion technology is clearly highly developed, even for low-end applications, and yet landspeeders and fighters make use of some kind of chemically volatile fuel. The Rebel base uses a safe and stable power source equal to any starship's.
Luke warms himself with a "small fusion furnace" on icy Hoth. It's a small portable heater, and as a small portable heater, it operates in the kilowatt range.
It is clear from this that fusion is not only considered a feasible power source, but is highly compact and safe for the user, representing long years of refinement. The size and power of Luke's fusion powered portable heater suggests the use of fusion for powering droids, vehicles of all sizes, and even hand weapons.
The landspeeders seen skimming about in Hoth clearly have a fuel that is flammable in an oxygen atmosphere; this is demonstrated in their destruction. Seen in the film and described in the novel is what cannot be anything but an explosive effect. Why would a vehicle many times larger and more expensive than Luke's fusion heater use a volatile chemical for fuel?
As the shields of the Rebel complex could completely block the Imperial fleet's fire, while Imperial Star Destroyers remained vulnerable to ion cannon fire from the ground, we may suggest incidentally that the Rebels either had access to superior technology or a superior power source than a typical Imperial Star Destroyer.
Whatever power source it is does not appear overly volatile. When the Rebels' power generator is destroyed, it involves a distinctly sub-nuclear scale explosion. The generator also does not seem noticably larger than those an ISD could carry, suggesting that Star Destroyers are not overgunned or shielded for their size.