ftr - some electrical devices may be more prone (sensitive) to a power dip than others.
You should still try to get this Prisma replaced but it is possible this thing is a tad more sensitive to an ever so slight change in the voltage.
For future readers just refuse to accept these cheaper things as the DME gets paid the same whether you gets this or a Resmed or a Philips even. The DME will push these on anyone they feel they can.
You can always insist your Dr write the brand you want and "No Substitutes" on your prescription.
AND also get a copy of this prescription *In Your Hand*.
The DME wants it sent electronically but it helps for you to see what it reads and just in case you have to go elsewhere.
The Prisma (by Lowenstein) is not a "cheaper thing" - it's actually a quite expensive machine made in Germany. FWIW a member of another forum I subscribe to is a technician who services and repairs these machines - he rates the Prisma very highly for the quality of construction and materials.
Back to the OP's problem - apart from a power failure it sounds like something that needs to be fixed or replaced under warranty.
IMO
You should still try to get this Prisma replaced