A TDA7293 amplifier module is constrained in four different ways (from the datasheet);

1. Supply voltage is +/- 50V maximum

2. Built-in current limitation of 6.5A maximum

3. Module heat dissipation of 50 Watts per module (150W total)

4. Additionally, in modular (parallel) mode, the TDA7293 must have the supply voltage derated so that the power heat dissipation per device doesn't exceed 50 watts. The supply voltage derating depends on load resistance. The supply voltage has to be less than +/- 50 V for a 6-ohm or greater load, less than +/- 42 V for a 4-ohm load, less than +/- 30 V for a 2-ohm load, or less than +/- 21 V for a 1-ohm load.

I'm going to be driving a 4-ohm speaker (rated 300 W RMS), so my supply voltage will have to be less than +/- 42 V.

I have two 120 V power supplies on hand at the moment.

One gives +/- 36 VDC @ 3.0 Amps (216 VA)

The other is +/- 36 VDC @ 6.0 Amps (432 VA)

My question is:

Do you add up the maximum amplifier output (250 watts) plus the maximum power heat dissipation (150 watts) to determine the minimum VA requirements of the power supply?, so that 250 + 150 = 400 watts minimum?

If not, how are you supposed calculate the size of a power supply?