Microwave oven capacitors are generally rated for about .1 microfarads, 1800-2000 volts. In fact, they are often charged with DC in the microwave. The magnetron requires around 4000 VDC. Since the transformer puts out around 2000 volts AC, the cap and a high voltage diode are wired as a voltage doubler. The cap charges through the diode (DC) and discharges into the magnetron. You should be able to charge the microwave capacitor with DC just fine.
How many do you have? If this is for your Tesla coil, you will probably need a lot of them to match your transformer
If you're working on a capacitor bank,
this site may help you. It gives you a lot of the equations that you'll need.
I hope it's ok that I'm assuming you're still working on a tesla coil
Good luck!
Der Strom