Guide to Pico-PSUs
So what is a Pico-PSU? In the simplest terms, it's a way to have the PSU be external thereby saving tons of internal space. They are generally low powered (less than 160W) unless you start doing some custom wiring.
There are two parts for Pico-PSUs.
The AC-DC converter (aka the brick).

The DC-DC converter (what sits inside the case).

Things to consider:
The AC-DC converter needs to match the specs of the Pico-PSU. If the DC-DC converter can only take 12V makes sure the AC-DC converter outputs to 12V. This needs to be mentioned because many bricks will output to 19V instead of 12V. There are some wide voltage Pico-PSUs that can take a 19V but just check to make sure.
It needs to be the level of the Pico-PSU if you want to use full power although it isn't required. A 120W Pico-PSU can be mixed with a 102W brick for example. The max power is determined by the weakest link in the chain, whether it be the brick or the pico-PSU.
Lastly, high wattage AC-DC converters will utilize a 4-pin din jack instead of a single pin like what is pictured above. This is used for plugs that need greater than 9 Amps.

The most common Pico-PSUs go:
120W $39.95
150W $45.00
160W $49.50
There isn't much difference in price between them so I'd probably just go with the 150W. Note that the 120W is a 20-pin while the 150W and 160W have 24-pins. Also the 120W doesn't have a 4-pin mobo connector. You have to buy a 4 pin splitter and attach it where the wires come into the case.
If you go 150W get this power brick.
The low wattage 60W/90W are really meant for Zacate (E-350) or Atom builds.
Prices for these are probably cheaper if you look around. I just wanted to use a central location for parts. Good luck.
There are two parts for Pico-PSUs.
The AC-DC converter (aka the brick).
The DC-DC converter (what sits inside the case).

Things to consider:
The AC-DC converter needs to match the specs of the Pico-PSU. If the DC-DC converter can only take 12V makes sure the AC-DC converter outputs to 12V. This needs to be mentioned because many bricks will output to 19V instead of 12V. There are some wide voltage Pico-PSUs that can take a 19V but just check to make sure.
It needs to be the level of the Pico-PSU if you want to use full power although it isn't required. A 120W Pico-PSU can be mixed with a 102W brick for example. The max power is determined by the weakest link in the chain, whether it be the brick or the pico-PSU.
Lastly, high wattage AC-DC converters will utilize a 4-pin din jack instead of a single pin like what is pictured above. This is used for plugs that need greater than 9 Amps.

The most common Pico-PSUs go:
120W $39.95
150W $45.00
160W $49.50
There isn't much difference in price between them so I'd probably just go with the 150W. Note that the 120W is a 20-pin while the 150W and 160W have 24-pins. Also the 120W doesn't have a 4-pin mobo connector. You have to buy a 4 pin splitter and attach it where the wires come into the case.
If you go 150W get this power brick.
The low wattage 60W/90W are really meant for Zacate (E-350) or Atom builds.
Prices for these are probably cheaper if you look around. I just wanted to use a central location for parts. Good luck.
I can't run my A8 with a 6870 without it force shutting down halfway through a game. I've yet to test it with a lower power CPU so it might work if I had a 35W CPU. Maybe not at 100% load for both.
I'll edit and write up some more about power bricks and the Pico itself.
@minnetonka16
im sure a amd apu cpu would be fine even with a lower end gpu.
the apu cpus are something like 20 - 100watts?
a average cpu is what 65 - 125watts? so yeah should be fine with a 160+ watt pico psu?
eg. a gt 640 and 65watt cpu? should run alright on a 120watt psu. depends which cpu to which psu. but yes will run fine
Specifically with i3 setup?