Assuming I understand what you said or what you really want to say,
the total power power consumption of your class D power modules is
20W.
As class D switching amp assuming it is some typical pulse width modulation (PWM) design, the power stage should get a 90% efficiency.
Factoring into the PSU efficiency, I suggest (correct my assumption if deemed neeeded), the AC power needed to power your power modules would be somewhat 25VA.
A beefy PSU is always helpful. But for class D switching amp for audio use (assumed so since you did not mention specifiically), I don't think you need overkilling due to its relatively low power consumption.
So to answer your question, you may want to custom order an power iron of 25-30VA if off-the-shelf standard product is not available.
I know a brandname 2x500W class-D audio power amp only use basic CR filters & the heat sinks are very small, due to its 82% power efficiency.
c-J