Just wondering if I could charge my 12inch macbook with the type-c adopter that came with the Nintendo switch
I have tested on the 2015 MacBook 12". Works perfectly. Charges at 15.3V @ 1,9A = 28,7W. The MacBook 12" charger also works on the Switch.
USB-C and recent USB Power Delivery standards make this a fairly safe bet in terms of cross platform interoperability. As long as the charger or cable aren't knockoff, you should expect reasonable results mixing vendors.
Reasonable is a 15 inch MacBook Pro clearly won't run and charge from a 30 watt adapter (whether Apple or Nintendo), but if powered off, it will slowly and safely charge itself at the rate the connected adapter provides.
Just an important pointer for anyone considering to charge their switch with non nintendo chargers!! Watch out, using the non-nintendo certified chargers have a real chance of completely bricking your device.
The switch charging standard is not completely the same and using a different charger could render your switch useless.