Cascadia 12v sockets won't output their rated output unless the engine is running

Question for ya'll, I have a 2012 Cascadia. My laptop has a large 180w power adapter. I drive for Schneider so hard wiring an inverter to the battery is not an option. On the passenger side of the bunk there are two 12v sockets, the upper one is rated 12v @ 10 amps (so 120w) and the lower one is rated at 12v @ 20amps (should be able to supply 240 watts).

Plugged into either the 12v/20 amp socket or the cigarette lighter socket, I have no problem using my laptop when the engine is running. If the engine is turned off, however, the 12v outlets don't seem to output enough power, the inverter will cut in and out if I'm doing anything on it that requires it to use the dedicated graphics card and not the onboard graphics chip built into the processor, like playing a game. I've tried this with both an inverter rated at exactly 180w and a slightly larger one as well. Both have the same issue. Connections in the sockets seem solid and there is no wiggle room.

Like I said, Schneider won't allow any inverters to be wired directly to the battery, unless you have a CPAP machine and they install the inverter for you. I don't have one. The largest inverter they allow us to use is 180w.

I was looking at the sockets under the lower bunk, it looks like each is wired individually, so each appears to have its own fuse.

I was considering purchasing two 12 plugs and splice the 2 positive wires together and the two negative wires together and then connecting this "Y-cable" to my inverter. Perhaps between one 20 amp socket and one 10 amp socket I would be able to get enough juice to the inverter when the engine isn't running?

Any suggestions would be great... I'm sure my laptops power adapter isn't too happy with me so far.

 

Makes perfect sense now that you say it.

And now for the best part:

I was bored so while waiting to read yalls replys I went into the Flying J and bought 2 cigarette lighter plugs with CB radio power connectors, and a cheapo wiring kit that came with a crimper and connectors. Never thought to bring my electrical tools with me in the truck ....

Walked back in the truck, and while chowing down on my Flying J chicken fingers and macaroni I cut the CB power leads off each plug, and then spliced both positive together and both negative wires together (separately, of course). Next I used my cheapo crimpers to crimp on a ring terminal to the positive and negative wires, then connected them up to my slightly larger inverter that I will not mention what the wattage is for... umm... reasons. Plugged in my 12v plugs to the 10a and the 20a connector below the bunk, fired up my laptop and ran Furmark to stress the GPU to the max and make it draw full power from the inverter and...

... it works perfect now without the truck running since it can draw from both the 10a and the 20a socket.

LOL I love redneck engineering. Though I will always remember to unplug this when I'm not using it in the truck just in case... xD