Can I use the MagSafe 45w cord (just the wall 3-prong) with my USBC 61w adapter?

Yes, a grounded extension cord.

Shouldn't be a problem. That's simply a universal part that should work. Even an ungrounded 2-prong cord should work. I had one of those in the box with my 2001 iBook. Apple doesn't bundle those extension cords any more as far as I can tell.

You can use any extension cord.

mindblur wrote:

Basically I just want a longer power cord. Can I use the old 3-prong wall cord and attach it to the 61w USB-C adapter block?

Thanks.

You can always buy another one if you have some resistance.

https://www.apple.com/shop/product/MK122LL/A/power-adapter-extension-cable