Dark energy is energy that is associated with the vacuum itself. It interacts gravitationally just like any other energy, but it can't move around like free energy. It has a fixed density. The net effect is that free energy objects are repelled. (Recall the rising bubbles.)
Alan Guth exploited this effect in his inflationary cosmology: the vacuum energy density comes from the "false vacuum". What quenches this expansion is that the false vacuum decays into the true vacuum, and the extra vacuum energy density turns into the free energy that makes up all the galaxies, Pokemon cards, ring bologna, etc. That should convince you that it's the same "stuff" as the energy that comes out of your outlets.
So you see, it's really the same stuff; we call it "dark" energy because it can't shine (i.e., move around) like light can.
How is this energy tied to the structure of the vacuum? That's anybody's guess.
The cosmological constant problem predates the recent evidence for dark energy. However, dark energy raises a new puzzle, the so-called coincidence problem. If the dark energy satisfies (can’t type it, but it would be critical density of dark energy at 0.7), it implies that we are observing the universe at the special epoch when (critical density of matter) is comparable to (critical density of dark energy), which might seem to beg for further explanation. We might rephrase these two problems as follows: (a) why is the vacuum energy density so much smaller than the fundamental scale(s) of physics? and (b) why does the dark energy density have the particular non-zero value that it does today? If the dark energy is in fact vacuum energy (i.e., a non-zero cosmological constant), then the answers to these two questions are very likely coupled; if the dark energy is not due to a pure cosmological constant, then these questions may be logically disconnected.
In recent years, a number of models in which the dark energy is dynamical, e.g., associated with a scalar field and not a fundamental cosmological constant, have been discussed… These models, sometimes known as “quintessence” models, start from the assumption that questions (a) and (b) above are logically disconnected. That is, they postulate that the fundamental vacuum energy of the universe is (very nearly) zero, owing to some as yet not understood mechanism, and that this new physical mechanism ‘commutes’ with other dynamical effects that lead to sources of energy density. This assumption implies that all such models do not address the cosmological constant problem. If this simple hypothesis is the case, then the effective vacuum energy at any epoch will be dominated by the fields with the largest potential energy which have not yet relaxed to their vacuum state. At late times, these fields must be very slight.
I'm predicting bondbonds. Yummy hypothesis.