Question 1: Can I get by with a c.400 watt PSU?
Question 2: Can anyone recommend a c.400 watt PSU that is, in order of priority, (a) exceedingly quiet, (b) efficient to at least 80+ standards (pref Bronze and up), (c) is available in the UK at pref <£60 mark. edit: preferably modular or semi modular cabling and a sub 170mm length too
Question 3: Have I forgotten any significant power draws below?
Partial upgrade incoming, replacing an elderly but still suprisingly capable (but oh so power hungry and noisy) ATI HD4870 with a new shiny HD7770 (hopeful result being modest performance boost, huge power and noise savings) and a system SSD drive (Samsung 830 128gb, now they're cheap). No-name PSU is also due a refresh due to being very noisy, both accoustically and electrically.
Anyhow, end system and TDPs will end up something like this:
i3-530 CPU - 75w
HD7770 GPU - 80w
3 * 120mm system fans @ 1.5w each = 4.5w
Samsung 830 SSD = 0.5w
2 * elderly WD Raptor 10k 74gb HDDs @ 15w each (striped as app drive) = 30w
DVD drive = 20w
Asus mATX m/board (h55/lga 1156 chipset) = 40w
Adding all those up we get a theoretical max in the region of 250 watts.
There are some significant guesses in there, the old Western Digital raptors will likely draw 50% more or so at spin up (but at that time other components won't be maxed, so no worries) - similarly, they may be drawing about 10w less between them during full-sparkle-shiny gaming time as everything's loaded into memory).
Motherboard power draw (independent of other components) is a complete guess based on limited googling, it'll be running onboard sound/networking and other motherboardy things.
Rough guess at a typical absolute maximum during gaming is 220w - basically the same as the calculation above but subtracting the DVD drive and reducing the app drive HDDs down to 10w each.
This makes me think a 400w PSU will be fine, putting likely max draw smack bang in the middle of a PSU's most efficient loading (50% of rated). The old HDDs will likely be replaced at some near future point for a single more efficient app drive (maybe a Seagate Momentus XT hybrid - http://www.anandtech.com/show/5160/s...rid-hdd-review) which should reduce power consumption by another 20 watts or so.