we’re planning to build up a small Jetson TK1 cluster (approx. 10-15 devices).
Therefor we want to use a common power supply for all devices.
On the Nvidia project page  they write that all kits have a “AC Adapter with power chord” included. Also the schematics of the Jetson  tell sth. about “AC Jack” (on p. 26). The community wiki on elinux says the opposite . They say, a DC connector would be required.
We didn’t order the devices up to now, so I’m not able to find out what I really need.
I’m a computer scientist and no electrical engineer - but does the TK1 really need a 12VAC power supply? I can hardly believe…
Jetson arrives with an adapter. Output is 12V DC regulated, input is AC. I think it says tolerance should be within 10%. The problem you will run into with a cluster is that you’ll need enough 120V AC outlets with surge protection! Or a well-regulated 12V DC supply (with enough current available for your cluster) and a lot of connectors.
Ah ok, great, thanks. I was sure that AC power supply is nonsense, but official documents are a bit inaccurate… Just wanted to make things clear.
I’m planning in bigger dimensions :-D
I’m going to use a Meanwell power supply. Probably sth. like Meanwell SP-500-12  12V/40A .
Datasheets say that one Jetson might consume up to 48W under maximum load + SATA drive and all stuff connected and as I don’t know exactly which periphery i will run later, i do a worst case calculation.
You definitely don’t need to assume you will use 48W per Jetson unless in a very extreme case. A much more realistic figure would be 15-25W for the whole board including accessories, but it does depend a lot on the accessories. So far I haven’t seen my board use more than 12W of total power (ie: 12V @ 1.0A) even with a few USB accessories & Wifi plugged in while running intense CPU + GPU code (see actual figures at http://elinux.org/Jetson/Computer_Vision_Performance#Power_draw_during_computer_vision_tasks). But I haven’t tried SATA. If you will be plugging in SATA spinning hard-disks or a mini-PCIe add-on card or a big USB device (eg: external spinning hard-disk), then I would add 10W for each of these to be safe.
So for example, if you will have 15 x Jetson TK1 boards connected together by Gigabit Ethernet (let’s say it adds 2W per board), each with a SATA hard-disk plugged in directly to the board, and will get all boards to run intense CPU+GPU optimized code, then I would use a power supply that can handle a continuous output of 15 * 27W = 405W (15W for each board + 10W for each SATA disk + 2W for Ethernet). So a 500W power supply should handle this cluster of 10-15 Jetson TK1 boards + SATA drives, but if you think you are more likely to use 15 boards than 10 boards then it might be worth spending extra to get a 600W instead of 500W, since you want some extra power to handle peak workloads such as on initial power-on that always causes a short spike in power draw.
The cheapest option if you will use upto 10 x Jetson TK1 boards is surely to use a cheap PC power supply ($10 - $50 depending where you look) that gives atleast 400W (to add some margin on top of 270W) on the 12V wire. (Note that PC power supplies put some power into 5V and some into 12V, so you should look at how much power goes into the 12V line and ignore the 5V rating).