In the case of your series-connected capacitors, George, the voltage rating will be double, however, the capacitance value will be half, assuming indentical caps.
In the case of the transformer, the output voltage will be the sum of the two secondaries or it will be zero! I depends upon the phasing of the connections of the secondary and primary. If like primary wires are connected together, the primary will be in-phase. If the secondaries are connected in series with "unlike" ends connected and the other "unlike" ends used as the output, you will effectively have an 8:1 step-up ratio. But be very careful doing this, for you can get into some pretty high voltages. Also, the transformer's voltage ratings (e.g., secondary-to-primary differential) could be exceeded and the transformers will arc over between windings. That's the down-side of it all.
Dean