The outlet and plugs will add whatever resistance/voltage drop they add regardless of the extension cord size.

I just didn't see a reason to use #10 wire for an extension if my house is wired with #12, but already said that's my opinion. I didn't look at voltage drop versus current vs run length of wire etc.

Randy

Each piece of wire adds it's own resistance. The total resistance is what matters and if you use 10ga for some part of the whole the total resistance will be lower and the voltage drop/power loss will be less.

exactly that, I usually shiver when folks write 'umbrella warning' statements but with something like a relatively high power piece of kit only folks who know what they are doing should be considering DIY or better leave it to a qualified technician to solve the problem.