I have a couple of 50w 5A 12V DC Lipo/nimh chargers which are great because they are small and easy to take to the track.
They are the same standard sort of 50w charger with LCD display and 4 buttons such as an Imax B6 or a hobby king ECO 6 50W.

When charging Lipos, I only use 'CHARGE' or 'BALANCE' functions at 1C. so if it charges 5A at 12v, thats 60W-already 10W over its prescribed limit.

Here's my question:
There is another function 'FAST CHARGE' which I have not yet used.
How does a 50W 12V DC charger that only goes up to 5A charge any faster than the regular Charge or Balance charge functions which are already drawing 50~60W?

Any light on this situation would be greatly appreciated!

Fast charge on a lot of chargers will cram the battery up to about 85%, roughly balanced, so you can get back out and keep playing. The last 15% takes the same time no matter what you do, due to the way Li* chemistry works.

Your charger doesn't charge the battery at input voltage. There is some postregulation going on to drop that down to 1V over whatever the current cell is at. LiPo's are charged by keeping the voltage 1V ahead of the cell until top voltage (Minus 1V) is reached. If you tell it 5A, it's definitely only getting 5A of input current.

Thanks WindDrake.

That makes sense to me.
so the fast charge doesnt necessarily get your battery to 100%, it just gives you enough to get out there if you are in a hurry before a race.

Cheers