Garmin Part 010-10723-06 : Authentic Garmin.  This power adapter is a perfect fit for your GPS.  Manufactured by Garmin.

Fits many models including:
Garmin Colorado Models: 300, 400i, 400c, 400t
Garmin eTrex, Summit, Venture, Legend, Vista Models: C, H, HC, HCx
Garmin Nuvi Models: 30, 40, 40LN, 50, 50LM, 200, 200W, 205, 205W, 250, 250W, 255, 255W, 260, 260W, 265T, 265WT, 275T, 370, 360, 350, 310, 300, 465T, 500, 550, 680, 670, 660, 650, 610, 600, 785T, 775T, 770, 765T, 760, 755T, 750, 885T, 880, 860, 855, 850, 1100, 1100LM, 1200, 1250, 1260T, 1300, 1350, 1350T, 1350LMT, 1370T, 1390T, 1390LMT, 1450, 1450LMT, 1490T, 1690,2300, 2300LM, 2350, 2350LMT, 2350LT, 2360LMT, 2360LT, 2370LT, 2555LM, 2555LMT, 2495LMT, 3550LM, 3590LMT
Garmin Oregon Models: 200, 300, 400c, 400i, 400t, 450, 450t, 550, 550t
Garmin Streetpilot Models: i2, i3, i5
Garmin Zumo 220