Hello

Title says it all: I need to buy a 12V power brick to feed a 90W PicoPSU. The motherboard is an Asus AT4NM10-I (Atom D425 on board), and I'll need to connect a 2.5" SATA drive, and an external DVD drive through two USB plugs just to install Windows on the drive.

The Mini-box page doesn't say what AC-DC power brick users should use with that PicoPSU. I assume there's some loss between the 220V wall plug and what comes out of the power brick, so should I go for a 120W?

Thank you.

You don't need 90W for this. A 50W brick would most likely be fine.
You probably have such a brick lying around. If not you, your friends or neighbors.
But if you don't want to waste electricity, get an efficient brick. There aren't many good brick reviews and the ratings aren't very useful (except the very best ones) but I guess shopping by brand and rating is better than nothing. Ideally, you'd want a reliable meter to test the bricks yourself. Failing that, you can touch it as a sanity test: if the brick runs hot, it's wasting power.

Like HFat says, a small brick will do. 12V bricks rated for 5A (60W) is quite common and will work fine. I have a small diskless Atom system that I run with a 12V 2A brick but that might be cutting it close in your case.

Thanks. I'll get a 60W/5A. I got the 90W PicoPSU because it's the smallest they have.

I don't know much about electricity: How can we can get a 90W output from the PicoPSU while it's fed 60W from the AC/DC power brick?

Unless the brick performs a good bit better than its rating suggests, you can't.
Which is why you should take care not to use this brick with a computer which might actually draw 90W!

So the PicoPSU can provide up to 90W, so I should get an AC/DC brick that provides as much power as needed by the different components in the computer + some room to compensate for the loss converting the AC power to DC?

The AC/DC loss should be taken into account for the rating already (12V and 5A describe the output).
But there might be some DC/DC losses as well. In any case, the pico (or equivalent board) will consume a little electricity.

A problem is that some parts have power consumption spikes (when you power them up for instance) which are hard to measure. 3.5'' drives are known for this. The ability of your power supply and/or brick to deal with such spikes is hard to determine as well.

But in practice you should be fine with a reasonably low-wattage brick as long as it's not too crappy.
Vicotnik runs an Atom on a 24W brick and many of us have run desktop gear (such as Sandy Bridge dual-cores) on 60W or 65W.

Thanks for the info.