The power of attorney under which any contracts of insurance are exchanged pursuant to this chapter shall provide for a cash premium deposit and a contingent liability of the subscriber during each annual period of the term of each contract of insurance issued to the subscriber to be fixed in the power of attorney, but in an amount not less than one nor more than ten (10) times the amount of the annual portion of the cash premium deposit stated in the contract, except that exchanges which have a required surplus equal to three hundred fifty thousand dollars ($350,000) or to the minimum capital, if any, required of a stock insurance company transacting the same kind or kinds of business, whichever is greater, may issue policies without contingent liability; provided, that the exchange which shall have issued policies without contingent liability after the acquisition of the surplus may continue to do so only so long as it maintains a surplus in the amount required by this section, and no exchange shall issue any non-assessable policies, except during a time as it shall continue to maintain the surplus.