Everything said so far is correct, but just so you won't be confused/misled when reading certain power cord descriptions, please note the following:
Quite often, cords are described as "20 amp" cords even though they have 15 amp hardware (plugs). This is because the wire conductors themselves are 20 amp capacity. The only reason I can think that cords are sometimes described this way is to indicate that they are capable of powering high loads (like big amplifiers.)
Most audio gear (except for a handful of "big mutha" amps) have 15A IEC receptacles. And most wall outlets are the standard 15A.
The use of 20A wall receptacles would probably provide you better contact area and a floating ground option (which I don't think you can get with 15A outlets). It would also allow a bigger wire size for the house wiring. All these things can (possibly) improve performance. "Possibly" meaning, for instance, if you were over 25 feet from your main panel, you'd want to use maybe 8 AWG wiring in the wall to avoid voltage drops, and then you'd need to use 20A outlets to connect 8AWG wire.)
As Jea48 mentioned, 15A cord can be (as small as) 14AWG per conductor. And most code minimums for house wiring itself specify either 14 or 12 for 15A circuits and 12 or 10 for 20A circuits (usually the smaller of the two in each case.)
So, you may ask, why use cords with conductors that are bigger than what's in the wall? The answer is "Energy Transfer" And the more power a component consumes (amps) -- AND/OR -- a component's frequent need for "nano-bursts" of power (DACs are in this category) the more a bigger conductor size will contribute to improved sonics. OK, you say, but if my wall wiring is 12 AWG, what's the point of using a 10 AWG power cord?
Once again the answer is Energy Transfer. Let me state some obvious facts, and then try and provide an analogy: Alternating current is stored (in your wall) as a potential -- it doesn't do anything until you connect a load of some sort. BUT, that potential changes direction (polarity) 60 times a second. And the potential itself varies 60 times a second (from 0 volts to 120 volts) In other words, it's not really a "consumable" like natural gas, that gets burned up when it comes out the other end of the pipe (that would be more like direct current, where the battery eventually runs down ;~) No, AC just "sits there" and changes back and forth 60 times a second.
OK, so here's my lame analogy: let's say the house circuit is a reservoir (imagine the ocean) of energy that's constantly changing in pressure (potential) and direction (polarity) -- imagine the waves at the shore. When you plug your PC into the wall, it's like sticking a pipe into the ocean at the shoreline. The bigger that pipe is, the more accurately the potential and pressure at the other end (the component) will reflect what's going on in the ocean itself. OK, imagine the pipe gets smaller. The pressure at the other end is still the same, but if you use some of it to do some work, it'll take a second for the pressure to build back up (poor energh transfer). AND, if you add to that, the fact that the direction of the "pressure" (pushing in and pulling out) is supposed to change 60 times a second, then the smaller pipe is going to create a lag in polarity changing. That doesn't mean you're going to see 50Hz AC instead of 60Hz, it means that spots of frequency cancellation are created in the "pipe" which further keep the available potential (pressure) from being realized at the other end.
Moral of the story: Especially with 15A wall circuits (as opposed to 20A) and except for low power stuff (like TTs, phono preamps, tuners, cassette decks, CDTs, not DACS) use the biggest sized conductor power cords you can, even sacrificing fancy shielding and insulation for conductor size if you have to.
"It's all about energy transfer." -- Jim Aud, Purist Audio Design
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