Well I found this:
Isolation transformer. This is very important for safely working on live chassis equipment like line connected switchmode power supplies (primary side). You can build one from a pair of similar power transformers back-to-back (with their highest rated secondaries connected together. I built mine from a couple of similar old tube type TV power transformers mounted on a board with an outlet box including a fuse. Their secondary high voltage windings were connected together to couple the two transformers together. The unused low voltage windings can be put in series with the primary or output windings to adjust voltage. Alternatively, commercial line isolation transformers suitable for TV troubleshooting are available for less than $100 - well worth every penny.
But I worry about resonance between the two. Guess its easy to try
Would I be able to reduce resonance with caps a resistors between? This way it would interrupt any difference of potential between the two toroids? If I am not making sense its cuz I really dont know what I am talking about but it kind of makes sense to me.
Also, I found that the Tripath TK2350 Chipset can handle 42V easily. However I have not yet found any chips for sale.