The Dashavatara is a list of the so-called Vibhavas, or '10 [primary] Avatars' of Vishnu.
The Agni Purana, Varaha Purana, Padma Purana, Linga Purana, Narada Purana, Garuda Purana, and Skanda Purana all provide matching lists.
The same Vibhavas are also found in the Garuda Purana Saroddhara, a commentary or ‘extracted essence’ written by Navanidhirama about the Garuda Purana (i.e. not the Purana itself, with which it seems to be confused):
The Fish, the Tortoise, the Boar, the Man-Lion, the Dwarf, Parasurama, Rama, Krisna, Buddha, and also Kalki: These ten names should always be meditated upon by the wise.
Those who recite them near the diseased are called relatives.

— Navanidhirama, Garuda Purana Saroddhara, Chapter VIII, Verses 10-11, translated by E. Wood and S.V. Subrahmanyam
Apparent disagreements concerning the placement of either the Buddha or Balarama in the Dashavarara seems to occur from the Dashavarara list in the Shiva Purana (the only other list with ten avatars including Balarama in the Garuda Purana substitutes Vamana, not Buddha).
Regardless, both versions of the Dashavarara have a scriptural basis in the cannon of authentic Vedic literature (but not from the Garuda Purana Saroddhara).
The Dashavatara is a list of the so-called Vibhavas, or '10 [primary] Avatars' of Vishnu. The Agni Purana, Varaha Purana, Padma Purana, Linga Purana, Narada Purana, Garuda Purana, and Skanda Purana all provide matching lists. The same Vibhavas are also found in the Garuda Purana Saroddhara, a commentary or ‘extracted essence’ written by Navanidhirama about the Garuda Purana (i.e. not the Purana itself, with which it seems to be confused):
The Fish, the Tortoise, the Boar, the Man-Lion, the Dwarf, Parasurama, Rama, Krisna, Buddha, and also Kalki: These ten names should always be meditated upon by the wise. Those who recite them near the diseased are called relatives.
— Navanidhirama, Garuda Purana Saroddhara, Chapter VIII, Verses 10-11, translated by E. Wood and S.V. Subrahmanyam
Apparent disagreements concerning the placement of either the Buddha or Balarama in the Dashavarara seems to occur from the Dashavarara list in the Shiva Purana (the only other list with ten avatars including Balarama in the Garuda Purana substitutes Vamana, not Buddha). Regardless, both versions of the Dashavarara have a scriptural basis in the cannon of authentic Vedic literature (but not from the Garuda Purana Saroddhara).
Vishnu