Came across this on a jazz lead sheet and I have no idea what they meant by the plus. Is it an E7 with an augmented 5th? Is the 7th augmented?
This is a really not great way of expressing the following combination of notes:
E G# B# D Fx
In jazz parlance, a + at the end of the chord indicates #5. It is bad practice but it still turns up on lead sheets every once in awhile. I'm pretty sure the real book, for example, still has the turnaround at the end of the bridge of All the Things You Are written as C7+.
There are unfortunately many such old practices that makes reading older lead sheets more challenging than it should be. Another fun one is -10, which is what people would sometimes write before it was agreed that writing 7#9 made a whole lot more sense.