AC Power cords, which components 1st...?

If you are using a power conditioner with a removeable cord, then start there. That place affects the power for all the components in the system. I would do the CD player or DAC next; then the power amp. If you use a sub, then a better cord will usually tighten the bass.

The amp should be the first to get the upgrade.

According to David Blair at Custom Power Cord, the order of upgrading should be: 1) CD player 2) preamp 3) power amp. His power cords have won T.A.S. Golden Ear Award (Top Gun)! I highly recommend the Top Gun (there are three versions, depending upon the current draw of the component).` The entry level Model 11 is also an excellent choice if your budget won't let you spring for a Top Gun set up. Happy Tunes!

I agree with Sugarbrie ... at least as far as starting with the CD player/transport first, before the preamp/amp/integrated. The old saying about "garbage in ... garbage out" is certainly true in audio as well. If you send a dirty signal to the amp, you will just amplify the dirty signal. So, at least start with the CD player, and then work towards the end of the chain.
The same rule applies to purchasing components, you buy the best source component that you can afford. Then you buy the best amp you can afford. And last, you buy the best speakers you can afford. William Z. Johnson (truly a pioneer among audio manufacturers as the head of Audio Research Corporation ... and a most credible audiophile!) long before ARC had a source component to offer, and before the days of CD, made that astute observation. He said that you should start with the best cartridge/tonearm/turntable you can afford, and then buy the best preamp, and so on. That statement in the context of things, was a very honest approach to starting someone on the right foot in audio!
The only reason I hesitate about making the power conditioner the first component to replace the power cord is because it should be cleaning up the line voltage within itself. But, I won't argue that point until I've tried it myself ... I have tried the other and know!

Between the DAC and Transport which would be first.