All Phil will ever do, is bore people to tears with his juvenile whining.

Internet Turet's syndrome maybe. But I am not going to dwell on that. The only real power Phil has is that every once in a while he has something to say so people don't completely ignore him YET. Whatever.

"Wouldn't increasing the capacitance from 0.68uF to 1uF result in a 50%
increase in cooking energy? "

No, that is a common misconception in the business. Do you remember the formula for capacitive reactance ? Apply it and just guess the frequency is over an octave above the sonic range.

The fact is that those caps are not being used as reactive components like in a tuned system, they are being used as coupling caps.

In that circuit they are effectively in parallel. Ground and the power supply rail are effectively at the same AC potential, so it's not 0.68, it's aready 1.36 uF. That is almost a piece of wire at 20 Khz. Almost, but we are dealing with a quite higher frequency here.

I got some pretty beefy 1 uF/400 V here but they are old and I can't be sure they can really handle the current. Actually I would like to use them in speaker crossovers someday.

Anyway, people also make this mistake working on SMPSes. Some use a coupling cap to keep DC off the transformer, OK, but that is a coupler. Think about it a sec., it LOWERS frequency to produce more output. Letting the capacitive reactance curve into that would fight against what you want to accomplish.

"Now i'm stuck at finding the polypropylene caps. "

Digikey doesn't have anything ?

What are you dealing with here, rectified 240 volts ? At 320, 17 amps is 5,440 watts. Four burners would add up to 68 amps. What size breaker does this thing take ?

It is possible that they are special caps of course. Manufacturers love using special parts.

Either way, lots of that type of cap fail by exhibiting leakage under stress. Same with the snubbers.

When you get a circuit like that, treat is like a bridge rectifier. Balance.. You change all four diodes in a bridge right ? You change both outputs in an audio amp right ? Same deal here.

Also everybody think about why SMPSes with the "totem pole" configuration usually use full wave rectification on the secondaries. Because balance is as important as it is in an audio amp. It may not seem so, but it is. If not they would save money on diodes.