IT's a 1000W that came with the case - CoolerMaster (branded).
I notice today, whilst attempting numerous restarts, that sometimes I can here a fan spooling up and down again (and again and again) whilst the boot process attempts....but I get absolute zero - other than a "No video" signal - on the screen. Not even the chipset name, 512RAM etc.
I also find that sometimes the subsequent switch off needs me to hold the button for 4 seconds - other times it is instant off (like a lightswitch).
"Curiouser and curiouser", said Alice to the White Rabbit.