Thanks, i must confess that on digikey, many PSU's offtheShelf of 4kW and more, are 3 phase input.
This one is single phase and 3000W input.....
https://www.meanwellusa.com/upload/pdf/CSP-3000/CSP-3000-spec.pdf...its 280mm x 178mm x 65mm = 0.00324m^3
The questioned size of 200m x 200mm x 79mm is 0.00316m^3 = 3160cm^3
....so its not that far off.
this 3kW one
https://www.xppower.com/portals/0/pdfs/SF_HDL3000-HV.pdf...0.305m^3
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Searching [>3999W & Single phase input] takes quite some doing on digikey...but reveals the following 4.9kW PSU
https://www.artesyn.com/assets/ivs_ds_1591841960.pdf?a=8ae629292cc593d996b2a70d782393c20eb251a2...its 280mm x 203mm x 127mm = 0.00722m^3
...but cost unknown to Digikey...just says "Active"......(which presumably means they see what they think you can pay?)
...so if volume scales linearly with power...then 4kw and single phase would be 0.00589m^3 = 5890cm^3......186% bigger than the questioned size of 3160cm^3 (just less than twice the size)
The Artesyn IVS PSU range seems to be the only 100-265VAC input 4-5kW output PSU on the market.
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This one is 3phase and 4kW
https://www.belfuse.com/resources/datasheets/powersolutions/ds-bps-tcp3500-series.pdf...Costs 2300£ and is 0.0035m^3
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I suspect that at 4kW and single phase, people probably go direct to China?
I wonder what the cost would be?.....100/1000/10000 / yr ?