My boat that has separate 2 120V inputs (1 for A/C and 1 for everything
else). I have only 1 plug in at my dock forcing me to switch between
A/C and power.

1) Why are those Y-adapters so expensive? They are around $250 which
seems like a lot of money considering there are no electronics.

2) I have 3 extra power cables. Can I cut off the plugs and splice them
together to make a y adapter? What would you use to splice and contain
it all?