Hi @mikewashburn
Thanks for your post!
The Roam takes a maximum of 2 Amps at 5 Volts. If you supply it with a more powerful charger, it will make no difference - it will still pull 2 Amps, and charge in the same amount of time. Devices only draw the amount of current they need - otherwise everything would burn out immediately after drawing the full power available through the socket. The voltage supplied would make a difference, but only in that you would damage the Roam if you supplied it with more than 5 Volts.
So, you can use a 75W charger, as long as it does not provide more than 5 Volts, but doing so would not increase your charge time.
I hope this helps.
"Common sense is the collection of prejudices acquired by age eighteen." - Albert Einstein