No, only to New Haven, CT. All trains NW to Boston have to change at New Haven to diesel.
That would be incorrect. New Haven was the end of the electrification done by the New Haven RR back in 1914 that extended to Hell Gate in NY.
From Wash DC to New Haven CT it is 11 or 12 kv 25 hz power. The remainder not electrified by New Haven was mostly done by The Standard Railroad of the World (Pennsylvania RR).
In the 1990's Amtrak spent the money to electrify the remainder of the NE Corridor from New Haven to Boston using a 25kv, 60hz supply.
"Amtrak operates a 60 Hz Traction Power System along the Northeast Corridor between New Haven, CT and Boston, MA." SOURCE
If you are interested in the older part of their electric train network see HERE.