Where to find SMPS Schematic for Car Tube Amp 12V to 400V ?

Looking for SMPS/PSU for car tube amp,  I need 400Volt DC.
anyone knows any schematic for this ?

I saw many 300 Volt, but I nedd around 400Volt DC.

anyone ever build Tube Amp for car ? with at least 8Watt output ?
I saw many are using 2 watt, but I need higher output.

cal.